If you didn't get any points for it, that means it was just a warning.
At any rate, I'm not super familiar with the rules in there but if you got a warning or an infraction, it was probably for posting a lot of welcome messages with no real content. (ie, posting almost the same message to every single thread or making a lot of short posts all at once) If you want more information, I'd contact the mod who gave you the warning to ask for clarification~