Roscoe,
Is that standard placard? If so, I don’t have it on my plane (admittedly, it has been repainted twice).
I did poke around yesterday, looked in the tanks with a flashlight (couldn’t get my lighter to work LOL) and saw that it is engraved “19 Gal” right on each tab. Kind of embarrassed that I posted the question now.
Jim
N9846U