Several good answers, no point repeating what's been said, let me just add:
As others have noted, if management finds out about your Easter egg, depending on the personality of the managers and corporate culture, they may chuckle and compliment you on your cleverness, or they may fire you for making unauthorized changes to the software, or anywhere in between.
BUT ... if it turns out that there's a bug in your Easter egg that causes something bad to happen, like it creates a security vulnerability or a customer loses data, the laughter is going to come to an abrupt end. Odds are that you just did a quick test of the Easter egg, and presumably never told the QA department about it so they haven't tested it at all.
Someone on here said to consider the best case and worst case from your personal point of view: You get a chuckle for a few minutes versus they fire you. Consider best case and worst case from the customer's point of view. Best case: they find the Easter egg and get a little chuckle. Worst case: they find the Easter egg and then the software fails. The probability that the customer will say, "Oh, I lost all my accounts receivable for the last six months, but that sure was amusing to see a picture of the programmer and a funny message. It was worth it." ... odds of that are pretty much zero. And if the result is that the patient whose life support system this software is controlling died, or two trains collided because you introduced a bug in the traffic control system, etc.
Hey, I've gotten in trouble for making unauthorized changes to software that really did improve the functionality.
Yes, I've put Easter eggs in software myself. I wouldn't do it again without clearing it with management.