The cachet on this cover is composed of the silhouette of a jazz quintet with their shapes filled in with the spines of a jazz LP collection. The band is set against the playfully-warped keys of a piano and paired with the 2011 USPS Jazz "Forever" stamp (Scott #4503).
I have to admit that I laughed out loud when I opened the return envelope containing my covers. I had no idea how tiny the postmark was going to be ("What is this? Jazz music for ants?!")
If I had known its dimensions, I might have scaled my cachet differently or added another element — but I still think the effect works.