Don't know what engine you run, but if it's a Mopar RB, this might explain it (from the Imperial Club forum).
"I have a 1967 Imperial LeBaron with a 440. I would appreciate it if someone could tell me what the cross symbol on the identification pad means. I have only seen this once before on a 440 engine that came out of a Dodge police car.
Reply from Rodger:
The Maltese cross means you have a bearing that is a different size. The cross should be followed by a number ( or two ). The number(s) will be the bearing(s) that have a different size. It can happen with any factory engine."