Most people don't expect upper bounds, though, when talking about estimations. I for one would appreciate a less-than or less-than-or-equal sign when this is truly an upper bound, as it gives me a better idea of what to expect of the actual number of results in relation to the estimation.
What do you mean? If all I know about a number X is that it is an estimate for Y, I would expect X to be an upper bound for Y 50% of the time and a lower bound 50% of the time.