My US friend found this on a tee shirt she thought she had lost some time ago. It dates from around 1990. I am told by Matthew Bayley that the design is probably taken from the 15th C sallet that was stolen from a Cornish church years ago. It was there as a funerary piece. Many helmets were stolen in the last century from unsecure churches. The design crops up in Burgundian tapestries.
Thank you for the information, Matthew.