If you had received an infraction you would know because you'd get a PM telling you what it is for (or at least that's what I'm told...I've never gotten one myself).
You can't see other people's infraction PMs, but you can see when someone else has received an infraction by looking at their profile. Click on their av, and pick the vBExperience tab. Under Sums, if the person has infractions it will say so in the same area where it says "Reputation" if they don't, there will be nothing.
Look at your own profile, you don't have any infractions. Now look at this guy's
https://www.rollitup.org/members/fellowes-117957.html
and you can see infraction points listed. I think each infraction is worth 100 points...