Hmm that looks like the cut is almost twisted...

This might not be your problem, but try using an office scanner to take the image of the sign - there are a couple of issues I can see with using a normal camera.

Namely distortion from the lens - no lens is perfect and each point on the sign is at a different distance to the focal point of the camera. Secondly is shadows, they can easily be miss-interpreted as part of the metal when converting the bitmap. A scanner will remove these two issues. Thirdly, try to scale in both height and width unlinked, as they're not always in scale with each other.

If you haven't got a scanner, try taking the photo against a white background from a distance, with good lighting and a long distance between the sign and the background so you don't get shadows. The distance between camera and object is useful because although the sign is small in the images, it minimises the distortion. The object should also be dead centre of the image.