Yes, the method Fazzel uses is probably the best way to go.

I've got a character with 5 tattoos on the upper chest/collar region, and I used a color math node, with two more color math nodes attached, the skin texture attached to color math node 2's  first value, and one tattoo attached to value 2, color math nodes 3 & 4 have a tattoo attached to value 1, and the next color math attached to value 2, and color math node 5 has the last two tattoos attached to it.

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If you're joking that's just cruel, but if you're being sarcastic, that's even worse.