Index instead of unique key

Hello!

When i enable log-queries-not-using-indexes on my.cnf i get a lot:

# Query_time: 0  Lock_time: 0  Rows_sent: 0  Rows_examined: 4687
SELECT signature, spaminess FROM antispam_spam_marks WHERE content_type = 'node' AND content_id = 1737;

You have a combination of content_type, content_id set as Unique key. Is it possible to set it as index?

Thank you.