How to Create a Signature in Mountain Lion Mail
You’d probably rather not type your whole signature every time you send an e-mail message, and you don’t have to with Mail in OS X Mountain Lion. If you create canned signatures, you can use them in outgoing messages without typing a single character.
Here’s how it works:
Choose Mail→Preferences or press Command+, (that’s Command+comma).
Click the Signatures icon in the Preferences window’s toolbar.
Click the name of the mail account you want to create this signature for in the left column (iCloud in the figure).
Click the little + sign at the bottom of the middle column to create a new, blank signature.
Type a descriptive name for this signature to replace the default name Signature #1 (BL Long in the figure).
Type the signature exactly as you want it to appear in outgoing messages in the right column.
Drag the name you’ve assigned this signature onto the mail account you’re using it with.
If you have more than one signature, you can choose the one you want to use as the default: Choose the account in the column on the left; then choose the signature from the Choose Signature pop-up menu.
If you have more than one signature, another cool thing happens: A Signature menu appears in new messages, so you can choose a signature other than the one you chose from the pop-up menu as the default.