Depends - what was the sign there for? Did exist only to tempt the PCs into using the haste scroll before they needed it or did it actually serve a real purpose iin the setting? If the former - you were really unjustifiably lame. If the latter, I don't see a problem with it.
I think that it is a valid style of play, but not one that I endorse. I try to work with my players to have fun, rather than deliberately take an adversarial stance. Somebody else in this thread suggested that an adversarial GM/Player paradigm is unavoidable, but they're wrong - not only is it avoidable, but there are entire games built around the idea of avoiding it.