Would "MKMYDAY" count?
Clint Eastwood might have that one already though. I don't have any vanity plates, but I have thought about getting my Ham radio call sign as one. It costs $25 and there is no renewal fee outside of regular registration. But the plates that I got originally still work fine. When my son bought an out-of-state car and had to buy new plates anyhow I pitched in and bought him the Ham radio plates- it wasn't like it was going to cost much more anyhow.