I think that you will hear that you may not use the sign. Most likely they will say that they own the sign itself. As far as the shape? .....nada. Here is a quote from an article by a Patent and Trademark law firm........
"When a background design used for the display of a word or letter mark is sought to be registered by itself, without the word or letter mark, the design may be registered without any evidence of secondary meaning if it is distinctive or unique enough to create a commercial impression as an indication of origin separate and apart from the remainder of the mark; conversely, if it is not distinctive or unique enough to create a separate commercial impression as a trademark, it may be registered only upon proof of secondary meaning."
Nike was able to trademark the "swoosh" because of it's unique shape and it had become known as the Nike symbol without the name "Nike" included in the display of the shape. Similarly...the "single cut-away" guitar design that has become synonymous with Les Paul /Gibson guitars.
I think your concern is not with the shape, but rather the ownership of the sign itself....if you really need to be concerned.