After a long-running legal battle a judge in Australia has ruled that Katy Perry has infringed the trade mark rights of an Australian fashion designer called Katie Perry. Katy Perry (the singer) sold clothes under her name when promoting her Prismatic Tour.
Katie Perry (the fashion designer) has a trade mark registration for KATIE PERRY and has been operating her eponymous brand since 2006.
Katy Perry counterclaimed to try to challenge Katie Perry's trade mark registration but this was unsuccessful.
This case shows that no matter how famous you are it is important to get proper clearance before using a trade mark to ensure you are not infringing someone else's rights.