It's not often that when one is walking around Hollywood Studios, one stares at the ground. After all, there's so much to see and take in in any of the Disney parks but there if you happen to do so on Sunset Boulevard, you may notice some imprints in the pavement that aren't just something random, but in fact a very small but intriguing piece of Imagineering detail that once again separates Disney World from any other park.
The stamp in the pavement here, refers to "Mortimer & Co", whose name refers to Mickey Mouse. Mortimer was initially the name picked by Walt Disney for the character that would eventually become Mickey Mouse. Walt's wife, Lillian, suggested Mickey and Walt went with Mickey instead. Mortimer later came back into the Disney lexicon as a "Bizzaro" version of Mickey that has appeared in various films.
The stamp is in the pavement because it's a faux company that helped create the city of Hollywood. Remember, that Hollywood and Sunset Boulevards (along with Echo Lake) comprise the part of the park meant to be the Hollywood of the 1930's and 1940's, and Hollywood is a city. Therefore, these stamps in the pavement are similar to what construction companies would do if they were contracted to do work in a city. The fictitious company pays homage to Mickey's origins and of course 1928 refers to the year that Mickey Mouse debuted.