My dear vaisnava,
Please accept my humble obeisances. All glories to Srila Prabhupada!

Couldn't tattoos, if gotten in the right frame of mind, be similar to applying tilak? Tattoos can be a devotee's way to showing the world that, "My body is a temple of the Lord to be used in His service."

Hare Krsna!

Your servant,
Narayani d.d.