Phineas and Ferb Easter Egg - Doofinshmirtz Triforce Wall

On the episode "Jerk de Soliel" after the part where Candace is talking to Jeremy with the parsnips, it'll then go to Dr. Doofenshmirtz's lab.
Look above the steering wheel near Doofenshmirtz and you'll see a red trifore above the wheel on the wall.