If you are poor, it might be better to buy at least some of the tattoos, where you don't mind losing a bit more of one stat, from the NPC - but for others, you should really use mammon.
For a prophet, the standard tattoos are -STR/+DEX, -STR/+CON and -MEN/+WIT. Notice that you may or may not get any of the first two, but that the third is pretty much a must if you want to cast at a good speed. Some combinations:
-5STR/+4CON (NPC) & -4MEN/+4WIT (Mammon)
-5STR/+4CON (NPC) & -5STR/+4DEX (NPC) & -4MEN/+4WIT (Mammon)
-5STR/+4CON (NPC) & -2MEN/+2WIT (Mammon) & -3MEN/+3WIT (Mammon)
This is because most prophets do not actively engage in the fight - if you wish to do this, of course you might change a different set of tattoos.
For a warsmith, you will want tattoos that increase STR and possibly even DEX for PvE, to maximise your damage output:
+3STR/-3CON & +2STR/-2STR, +4DEX/-4CON is a pretty common choice, or the same with only one tattoo of +STR/-CON at +4/-4.
Later on in sieges, if you have to summon, it might be good to raise CON instead - I'm not sure.
You can get 3 tattoos total after 40 (I think it's just 2 when you're below 40).
For the prophet I'd go +4 wit -4 men, +4 con -4 str if it's a 2box -or actually played, but not going to be fighting.
Not sure about WS, it's a personal choice. But of course for better killing +4 str -4 con, the opposite for better survivability :p (but that's a bad nerf if you want to do any damage - you don't specify what you want to achieve with the tattoos) I guess I'm not much of a help here.
You can get 3 tattoos total after 40 (I think it's just 2 when you're below 40).
For the prophet I'd go +4 wit -4 men, +4 con -4 str if it's a 2box -or actually played, but not going to be fighting.
Not sure about WS, it's a personal choice. But of course for better killing +4 str -4 con, the opposite for better survivability :p (but that's a bad nerf if you want to do any damage - you don't specify what you want to achieve with the tattoos) I guess I'm not much of a help here.
WHat would you recommend for a Prophet that does PVP & solo (using heavy) as tattoo's?