Sometimes looking at the location with different light sources, is how I saw my VIN on the frame. I sanded the rust very gently and got the area smooth enough, but still pitted from the rust. I used a couple different flashlights and position of the flashlights to find the sneaky numbers on my 1924 Touring. I also tried to do a pencil rub of the area, no luck. Use a LED, and/or regular light bulb drop light and/or a COBB flashlights I hope this helps a little