A system of signatures, like that of financial deposits, is intended to ensure that all those who present themselves as candidates for public office will do so in a serious spirit.  Candidates who wish to be included on the ballot must, under the signature system, collect a given minimum number of signatures in support of their nominations.  The practical effects of this will depend on the number of signatures that must be collected, the time available to would-be candidates to collect them, and the care taken by the electoral authorities to ensure that the signatures are genuine and valid.
In some countries, the requirement that a nomination must be signature-supported  applies only to independent candidates, or to candidates representing a political party without a track record of support in a previous election.  The reasoning is that candidates representing parties that have shown themselves in a recent election to be serious contenders are themselves likely to be serious, and should be permitted to run for office without hindrance.  By contrast, barriers are needed to test the serious intent of independent citizens or representatives of new, untried parties who seek inclusion on the ballot.  The 'track record' of a would-be candidate's party may be decided according to a variety of criteria.  For instance, in Austria, the signatures of three members of the outgoing parliament are a substitute for the requirement of collecting several hundred signatures from ordinary voters.
The apparent advantage of requiring signatures, as compared with a financial deposit, is that it seems more democratic, insofar as it makes the qualification to stand for public office dependent upon public support, rather than on money.  However, there are several drawbacks.
Disadvantages of Signatures System
First, those giving signatures do so in support of the nomination of a candidate - that is, the inclusion of his name on the ballot.  Signatures need not signify that those who append their names commit themselves to vote for the candidate who is being nominated.  Hence, there may be a tendency for voters to agree to sign simply to end the conversation with a canvasser who appears on their doorstep, so they can get back to their cooking or gardening or (more likely) watching the television.  In other words, the collection of signatures may be a test of good organization rather than of public support. Moreover, good organization may be purchased with money: a candidate may pay supporters to collect signatures.
Second, notwithstanding the fact that signatures in support of a nomination do not automatically signify an intention to vote for that candidate, a signature system is open to criticism for being against the spirit of the secret ballot.
Third, if a considerable number of signatures are required, the system becomes complex, both for the would-be candidates and for the electoral administrators who must check the signatures.
In cases where elections are called at short notice, and there is a tight electoral timetable, the signature system may present an unreasonable barrier to those candidates who must collect them.  This applies in particular if the required number of signatures is large.  Representatives of political parties who are exempt from the requirement may then have an unfair advantage.
Examples of Signatures System 
Austria: Petition of three members of the national parliament, or 200-500 voters, depending upon area.
Belgium: Signatures of three members of the national parliament, or 200-500 voters, depending upon area (e.g. Brussels - 500, Antwerp - 400).
Britain: Ten signatures.
Canada: Petition of twenty-five voters in the district.  Written endorsement of leader is required for inclusion of party name on the ballot.
Denmark: Parties: representation in the outgoing Folketing, or petition of an equivalent of 1/175 of the total valid vote in the last election.
Finland: 100 voters.
Germany: Independents: 200 registered voters.  Parties with less than five members of the outgoing Bundestag. For state lists: one per thousand voters in previous election up to a maximum of 2,000.
India: One qualified voter.
Italy: Chamber of Deputies: 500-1,000 voters. Senate 350-700 voters.
Poland: 
The district (party) list of candidates for deputies should be supported by the personal signatures of at least 5,000 voters residing in the given electoral district.
 This requirement is waived if an electoral committee (party) has already obtained 50,000 signatures for other districts or has obtained 5,000 signatures in each of five districts.  There are special provisions for electoral committees representing national minorities. 
Russia: Duma: Nominees of electoral associations or electoral blocs nominating a federal list of candidates - 200,000 signatures of which no more than seven percent may fall in one subject of the Russian Federation.  Independent candidates 
no less than one per cent of the total number of voters in the electoral district ...In the event the election of deputies is held ahead of time, this number of voters shall be reduced by one half 14. 
The United States
The United States has regulations that are exceptionally burdensome to parties other than the Republicans and Democrats when it comes to access to the ballot. Katz describes the position as follows: 
The two established parties are given preferential treatment, while third party and independent candidacies actively are discouraged... Although only North Dakota explicitly guarantees the Democratic and Republican parties access to the ballot by name, all states except Mississippi and South Carolina guarantee a place on the ballot to any party with a specific share of voter registration or of the vote at the previous election... [I]n 27 states the requirement is at least 5 percent of the total vote cast, and in 11 of those the requirement is at least 10 percent. 
This means that small or new parties are obliged to obtain access to the ballot by a petition of signatures. 
In comparison to other countries, ... American parties and candidates are required to secure many more signatures ... Moreover, American nominating petitions may be subject to a dazzling array of technical requirements ... And when, as in Florida, a verification fee of 10 cents per signature is added to the requirement of petitions signed by 3 percent of registered voters, it is easy to understand why ballots in the resulting elections rarely include more than the two candidates whose positions are secured by their parties' previous voting strength.
 (pp. 260-61.)
Draft Only