Yes it's true; it's a piece of prænomen information which I was never aware as to. I've come across a late-nineteenth century document which reflects this 3-letter 'term', and then discovered through research at OneLook.com and Amazon.com that said term denotes the masculine name
Francisco. However, why is this so? At what time did this abbreviated form come into general use, and from what source? For a certainty it has been in existence for over 125 yrs now.