1970 (?) Schwinn Varsity. Decals - white/cream on blue paint - are nearly intact, but pretty dirty. What can I use to clean them that won't damage them?

The one on the seat tube looks almost like a paper label, but feels like a decal. The script on the down tube I cleaned the end where there is some some paint damage with Simple Green and it seemed to clean up pretty well. But I don't want to use anything that will cause long-term deterioration.