He was out on the town with his Slytherin sidekick Vincent Crabbe when he was spotted scribbling on the outside of the Auld Hoose, in Perth.
Proprietor Mark O’callaghan said he was stunned to discover who was responsible for tagging his establishment.
Families queued up to get selfies with the pair – and Percy Weasley actor Chris Rankin – at the city’s popular Riverside Light Nights celebrations.
The pair were later spotted having a drink at the Auld Hoose pub on South Street.
Mr O’callaghan said: “I had been planning to go along to the Light Nights to get their autograph, but couldn’t make it.
“Later, I got a call from the pub to say that Crabbe and Goyle were in. I asked if someone could get a photo of them to put on the wall, but they had had a bit to drink and the staff didn’t want to ask.”
Mr O’callaghan said: “I turned up for work the next morning and saw someone had written graffiti on two places outside the pub.”
The tags, written in white marker, appeared to read “Lurch” and “Bully”.
“I didn’t get a chance to look at the CCTV until Friday morning. I couldn’t believe who it was. I just thought: Surely not.”
Mr O’callaghan says the footage clearly shows Herdman, on his own, writing on the pub sign. He was earlier seen standing outside with Waylett, having a cigarette.
“I’m not going to report this to the police,” he said.
“I was annoyed at the time, but I can see the funny side. He didn’t leave any damage, and the tags came off fairly easily.
“It’s funny to think that people were queuing to pay £5 to get to see them and get their autograph, and I got mine for free.”
A similar tag appeared on the door of the neighbouring Sweeney Todd barbershop.
Herdman has been made aware of the CCTV footage and was asked to comment.