Google-contacts – Add a date field to a Google contact without year

While Lipis' answer still works, there's another method as well.

With the message open, hover your mouse pointer over the sender's name. An info card will pop up. If the address is not already in your contacts, you can click the "Add to Contacts" button to open a contact edit form with the name and email address already filled out.

(The Add and invite button is for adding the person to your Google+ Circles.)

Signatures are tied to the from: address you're using. You can use so-called "plus addressing" to define multiple different addresses that are actually just your address and assign signatures to each.

Here's an example:

1. Go to Settings | Accounts and Import
2. Click "Add another email address you own"
3. In the Email address: field, put username+mom@gmail.com
   • Normally you'd have to verify this address, but Google is smart enough to know that this is just your regular address
   • Obviously, put your actual username in instead of "username"
4. Go to Settings | General and go down the the "Signature" section
5. Change the dropdown to be the email address you just created
6. Modify your signature to whatever you like
   • How about "I love you Mom!"?

Now, when you send a message to Mom, just be sure to change the from: address to be the special address for Mom. Then your custom signature will be included.

One nice feature is that when Mom replies to that address, assuming you have turned on "When replying to a message: Reply from the same address the message was sent to" when you reply back this address will already be selected.