We use a stamp & a letter as well. Here is the sample language on the stamp.
Recipient/Endorser of check agrees to perfect
a lien in favor of __Your Bank Name___
directed by applicable state law, and to hold the Bank
harmless for all damages(including attorney fees) for any
preference actions or claims related to the perfection of the
Bank's lien, including but not limited to claims of owners,
third parties, and bankruptcy trustees.