Function can be patented. Form cannot, unless the form provides function. Form can be Trade Marked, even and especially if it has no function, but trademarks need to be very specific. I cannot see how a whole knife design could be protected by trademark. The name and logos are another matter. Example, Spyderco could not get patent protection for a simple round hole opening feature, but they could get the round hole recognised as a Trademark, but they had to use it on all their knives, even the fixed blades.