This Company is referred to by The Fix part of Heroes Season 1
A pamphlet featuring this company is given to Hiro Nakamura and Ando Masahashi by Kaito Nakamura's assistant.
Gannon Car Rentals is a fictitious company used in multiple TV shows (mostly NBC). Seeing this brand does not necessarily show a connection or reference between shows. It is simply a name and logo that the studio's legal department has cleared to be used with no copyright or trademark issues.