1) Go to the #bot-talk channel in Discord
2) Type:
3) Receive an Imgur link for your AV if you had one, or a saucy error message if not.!av <username>
Capitalization is not important, but if your username had spaces, include them.
If you aren't on the Discord, you can also ask here and someone who is might post the results for you.
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Now sigs too!
!sig <username>
The sig database is complete, so try it even if it didn't find your avatar.