Rose Tyler's TARDIS key

Rose Tyler held possession of a TARDIS key.

The Ninth Doctor gave it to her after she grew concerned he might leave her on Earth. It later glowed when he returned to the Powell Estate from Albion Hospital. (TV: Aliens of London)

Rose later gave the key to Adam Mitchell in case he wanted to wait in the TARDIS whilst Rose and the Doctor explored. It was almost stolen by the Editor when Adam tapped into the Satellite Five computer systems. Cathica Santini Khadeni was able to override it, however. After the adventure had concluded the key was snatched from Adam by the Doctor, and he was returned home. (TV: The Long Game)

When Rose and the Doctor had an argument regarding Rose saving her father, Peter Tyler, the Doctor angrily requested that the TARDIS key be returned, to which she complied. He later admitted he would never have left her in 1987. (TV: Father's Day)