Amazing Tattoo Ideas describes two cross tattoos designs for the forearm. One is in black ink with a complex design and a circular motif connecting the arms of the cross. The second is a wooden cross in brown ink with a banner around it reading "Immortal Through Christ" in nude.
Tattoo Short List also provides many examples of cross tattoos that can go on the forearm, including crosses with dragons, cross-shaped scars, crosses with angel wings, crosses made of wooden stakes and simple linear crosses. Other examples include larger images of which the cross is only a small piece or images that combine two independent images to make a cross.