property release is a different story. It's only needed if the user would want to use the picture in a commercial context, where you would be taking a 'free ride' on someone else's product/brand/building (lots of them in the picture - so it would mean tons of forms to be signed - impossible in this particular case).
If the picture in question is used in an editorial context (i.e., not advertising another product) - normally no property release is needed.
BTW, same would apply for all the faces/people - you would need a model release.
I hope the design firm who wants to license the picture from you - knows that. Otherwise better confirm how they want to use the picture