The Doctor and his TARDIS have been around for a long time. 50+ years in our time, almost a thousand for him. Maybe more. It makes sense that over that period of time, the TARDIS key has evolved. As I type this I have the 4th Doctor’s key in pocket, since I always carry it with me. Too bad I don’t have a Type 40 TARDIS to go with it. Well, now you can see them all in one place thanks to Deviantartist Terrasolo.
There have been all kinds of versions of the TARDIS key over the years. Some are normal, some are more alien.
It is actually amazing that most of these are normal looking keys, considering that it is a sci-fi show.