This key belongs to an OLD (not new like some have guessed) hotel access system from Kaba-Ilco named MARLOK.
The interesting aspect of this system: it combines electronic access control with mechanical keys. Here's a Youtube video showing it off:
The key is 'encoded' under those thin black strips. It doesn't use magstripes or weigand wires like some guess: the key is actually punched with a combo of holes. It looks something like this:
The reader in the door tries to pass IR light through the key. (The black plastic strips are opaque.) If the orientation of holes matches a valid combo, the door opens.
Unlike other Hotel Access Control systems, Marlok must be wired to a central database. Since this introduced a big cost, it was not very popular in the hospitality market and it pretty much died. Not only that, but the keys could not get dirty or soiled at all and still work. They had to be clean, and even a little dirt film could ruin a key or a reader.
However, there are examples still in use, and I believe Ilco still sells keyblanks for the system.