A 27.0mm post is good sign. It's means the frame is at least equivalent to tretubi SL (maybe tretubi SP, given the apparent frame size). You don't need to disassemble the fork to check for the spiral ridges. Just remove the front wheel and look inside the bottom of the steerer tube with a flashlight. They are only about 0.3mm thick bt 3.5mm wide, so look carefully. You may also be able to feel them with your finger.