This plugin will display member's signatures to Guests. 4.1, 4.2, and 4.3 compatible.
September 2020 Edit: I see people are still downloading this...
ACP - Members - Member Settings - Profiles - Profile Settings
Enable Signatures, and then one of the new options is to display to guests.
This plugin has not been needed at all for at least a year now, this is built in as of 4.4
I'll leave this around for now but eventually this will get culled. Obviously, this will not be available in the 4.5 ACP Marketplace, and, just as obvious, this will not be updated or supported.