Well this is all very funny, or sad, but the real reason females get there own code is that -
- it is useful to give a general description of whom to look for at a scene.
- yes, if police help is needed at a scene, it may be more urgent if it's a woman who needs help.
- you don't want to say "female" on the air, as idiots with scanners might hear and get there before the police do.
So the "x" codes, which may or may not have anything to do with the "x" chromosome, were born.
Where a numeric code is followed by a letter the letter is said over the air using the phonetic alphabet, so it would be "eleven-twenty-five x-ray". CHP even says "X-ray" instead of saying "female" or "woman" in normal speech with no number code before it, e.g. "The X-ray was driving."
http://www.policemag.com/cop-slang/x-ray.aspx