We can buy some

We can buy some and put them behind bars for vandalism.  

I model a period when graffiti was limited to chalk drawing such as Herby or Bozo Texino.

if you want to depict the act in progress

I've never seen taggers working in daylight so you'd need to be modeling the darkest hours of the night( then you could use cheaper figures) ......DaveB

caught in the act...twice

A two man crew, just me and yard foreman Rick working in the yards at Locust Point, back when the tagging crap was just taking off... we coupled to a track, and he walked back to make a cut, when he came upon a tagger who promptly vamoosed. he left a quality canvas bag containing numerous pockets and a shoulder harness...it was a bit heavy, as the bag's pockets were full of a variety of rattle can colors. Foreman Rick took the booty home.

About a month later, we went down to the same part of the yard to dig some cars out, and you know what happened...caught again!  Same as last time, the dude left another bag full of spray cans when he fled again.

I don't think foreman Rick had to buy any rattle cans of paint for a while. Oh, and we never saw tag-man again after that. It was getting expensive. I should mention that both encounters were on the day shift. 

I should also add that the tagger was working down in the middle of a freight yard, between tracks; he was not out in plain sight.

Neat....

Do  they have one in handcuffs?