Go to CafePress.com and do a search for Star Wars. *chuckle* Plenty of shirts with AT-ATs, speeders, lightsabers, jawas, Mos Eisley, etc. No idea how the Star Wars posters got accepted.
If you were using just MEPD: The Mos Eisley Police Department, or the 501st logo, etc.... probably won't be an issue. From a legal standpoint, if the average consumer could confuse your product/image with an existing product/image, then there is a challenge to the copyright or trademark.
The worst thing to happen is that they decline to produce the product and refund your money.
-Carl