Multiple realities
(covers information from several alternate timelines)
A red cross on Starfleet division patch
A red cross on the side of a vehicle
The red cross symbol was a red, cross-shaped medical symbol that was generally used to indicate something was medical related.
In 2258 of the alternate reality, an shuttle-like craft with a red cross on it was parked outside the Royal Children's Hospital in London. (Star Trek Into Darkness)
During the 2260s, the division patch on some medical nurses bore the red cross symbol. (TOS: "What Are Little Girls Made Of?", et al.)