Paint removal to find old markings

When I get down to painting my truck I'd like to sift through its history before applying the final coat. What methods have you used to remove paint by layer to reveal old unit markings and the like? Sandpaper/steel wool/other?

This has been a quest of mine for a while. I know my front bumper was replaced so the back is all i have left. I was going to try some 400 grit sand paper by hand but the fire dept that had my truck painted it and i dont see any paint brush marks on the bumpetts, so i'm thinking it was already sanded off. I have been able to detrimine where some of the manltence was done by the rebuild tags on components. FT POLK and FT HOOD. I have also found shipping papers stuffed in the seat coushins. From FT POLK to FT HOOD in 1992. I found out the 5TH ID mechinized moved from POLK to HOOD in 92 and 93 and became the 2ND armored. so mabye it was thiers. I just wish i knew what unit.