He doesn’t know how Dipper finds the mark, and frankly, he doesn’t really care. The kid can believe it’s a tattoo all he wants – better than trying to explain what it really is.
(It’s a mark of failure.)
Sometimes, Stanley Pines will wake up, phantom pains of burning flesh still lingering after thirty years.
He had to try and treat it alone, reaching around to the awkward spot on his shoulder to put on fresh bandages and burn salve he found in a first aid kit in the house. It never became infected, and it healed alright, but the mark of that symbol on the console never quite faded.
He was branded, as if he was livestock, a constant reminder of that night. And it was all his brother’s fault.
(But he started it, he instigated it, and it’s his fault Stanford disappeared into that damned portal. So. Who’s fault is it, really? Was it anybody’s fault, in the end?)
“I thought you said you didn’t have a tattoo!”
Because it’s not a tattoo. It’s a burn. A brand, reminding him of all his failures, all his mistakes, all the lies, and all the things Stanley Pines has ever come to regret.