Should Wikipedia and other wiki user signatures be required to be unadorned default?

Wikipedia (and other similar wikis) allows users to customize their signatures, including changes of font face and color, background color and choice of any text in the signature including non-alphanumerical Unicode code points, including smileys. Should that be allowed? Or should it rather be mandatory to use the default signature?

Arguments for

 * Too many users tend to create unseemly looking signatures. They choose garish colors, fonts, put bizarre labels on the links to their talk page, etc. This could be addressed by creating restricting guidelines, but the language of beauty is hard to make objective and prohibiting signature customization entirely is the one policy that is very easy to administer.
 * Other policies are very easy to administer, e.g. disallowed are changes in font face, font color, and background color.
 * That has to be administered/enforced, whereas customization of user signatures can probably be disabled technically.
 * The freely customizable signatures enable something like an arms race for whose signature is going to stand out more, resulting in some truly bad signatures.

Arguments against

 * Users should be allowed some room for self-expression. While it is true that some user signatures are very bad, this can be addressed by a guideline.
 * As argument for stated, the guidelines can be hard to formulate in a clear objective language.
 * Review of various polls and votes shows that most users do fine with default signature, without this form of self-expression.
 * Users have their user page for self-expression. Their user page is not copied to so many places, unlike their signature.