The sale is now over but recently someone was offering a "Mayline" HO tank car - also with a large stylized question mark on it -- on Ebay. Very possibly a Tyco car as well. If you act fast you could see the small picture,
Tyco was big into promotional trainsets for various manufacturers, not necessarily intended to be sold to the public but used as give aways and customer favors. I recent wrote an article about Johnson Wax cars (the prototypes) and mentioned that Tyco had created a Johnson Wax promotional trainset that included a caboose labeled Johnson Wax. I don't know if Johnson Wax sold these sets or gave them away to favored dealers and other customers.
Mayline was a respected manufacturer of office furniture for many years. The company has been acquired by another -- so it lives on perhaps as a brand but not a company. My guess is that either Tyco created a promotional trainset for Mayline (perhaps for their salesmen to use). Either that or someone who worked for Mayline decided to create a train, maybe to be used at some company event.
Tyco cabooses are, frankly, so commonly found at swap meets, often at almost give away prices (particularly the later ones that got very cheaply made), that there would be nothing special about this one. It can with a bit of plastic surgery (pun intended) be made into a more accurate model of the Pennsylvania RR's N8 class of cabin car, which is the prototype for aspects of the Tyco model but Tyco for reasons of its own scrambled the elements around to make it less specifically Pennsy; articles on how to do this have appeared in MR and more than once in RMC. Bowser's nice and more accurate N8 model in HO kind of killed most interest in the kitbash of the Tyco but at one time I laid in a supply of Tycos (on the assumption that I was almost bound to botch something in the process) and still have 'em, somewhere. I don't think I paid more than a dollar for any of them, and some of the shells I probably got for a quarter.
No longer a Pennsy modeler!
Dave Nelson