Manual:$wgMaxSigChars

User accounts, authentication: $wgMaxSigChars
Maximum wiki code length for customized signatures.
Introduced in version:	1.11.0 (r22960)
Removed in version:	Still in use
Allowed values:	(integer)
Default value:	255
Other settings: Alphabetical | By function

Details

Maximum wiki code length, in characters, for customized signatures. Preview versions of 1.10.0 prior to phab:rMWc52af0da6d7a used UTF-8 bytes instead of characters.

Warning:

This does not consider the length of the substituted templates used in the signature, so although {{subst:<Very long template name>}} will be rejected if the template name has more than $wgMaxSigChars (-10) characters, {{subst:Main page}} will work even if the main page is a lot longer than $wgMaxSigChars (T12715).