I saw this when I watched it weeks ago, but I only just now took some video stills. In the behind-the-scenes "Doctor Who Confidential" episode for "The Fires of Pompeii," which itself was titled "The Italian Job" due to the cast and crew having traveled to Italy to the world famous (to film students...) Cinecittà Studios to film most of it, I spotted this completely hilarious doodle on the wall. I don't know if it was already there once the BBC crew got there or if the crew drew it themselves out of boredom (which is highly unlikely, since there was no time to be bored on that shoot, what with the effects being delayed a day!). But it was funny to see.
These are the special effects guys loading the fake ash into a machine that will spit it out all over the actors in the street. Look behind them at the Warrior Woman drawn on the wall, Valeri XX, in her helmet and armor and carrying her shield--!