If this is truly porcelain, just use water and 000 steel wool. I have cleaned several signs with this simple process, I would be afraid the stripper might dull the color of the porcelain...
The color of
true porcelain enamel is part of the glass beads/powder itself, & the paint stripper & solvents wont harm it at all , ( think of a colored/stain-glass window pane, you can scratch it, break it, but the color is part of the glass itself, not only a surface coating) steel wool will work with some elbow grease too as you've stated.