I like #22, but I think the Image needs more definition. Is there anything you can do to make the WM & F stand out a little more? When I first saw it, it looked like XX.
27 looks better. It distinguishes between the W and M, but the F is still not clear. Can you get rid of the marks to the left side of the image, and make the F a bit more prominent on the rights side?
51 looks the best so far, but I would still like to to see a more recognizable "F" on the right side of the image. I would also like to do away with the two bars on the left side of the image.