dunno when you enlarge the picture it appears to be lines around the neck (by the cape) and around the wrists - maybe just a tight ass fitting suit. or one that is made to look like muscles etc - like some of Batman's suits.
Bellybutton ..that’s end game on the design shirt or no shirt debate here lol.
Mopar keep at it, dunno how you deal with the collectors here these days.
Edit : MINTAGE not vintage , in my OP smh