Such a setup of signatures is suited well for choosing one at random. Mac OS X Mail can do that for you automatically.
Insert a Random Signature by Default in Mac OS X Mail
To make Mac OS X Mail insert a signature randomly by default:
- Select Mail | Preferences... from the menu in Mac OS X Mail.
- Go to the Signatures tab.
- Highlight the desired email account.
- Make sure At Random is selected under Choose Signature:.
- Close the preferences window.
In Mac OS X Mail 1:
- Select Mail | Preferences... from the menu in Mac OS X Mail.
- Go to the Signatures tab.
- Under Select Signature:, make sure Randomly is selected.
- Close the preferences window.
For every new message you create in Mac OS X Mail, the program will now select one from all the signatures you have defined randomly.

