Late to the parade. But some observations.
The Spikes Dragon code is reversed handwriting. "Spikes Dragon Code". Good job spotting that!
The scrip shown on the newspaper from the older show looks like a nod to Galactic Standard and reads JIQUAY or something like that. It is not 100%. That an some other examples in FIM also bear a slight resemblance to the script used in the comics Erma Felna: EDF and Albedo. I worked on one of the RPGs for that way back and was pretty familliar with it after a while and it shares some styles with GS. But GS seems to be the more likely source for the appearancces.
So one strong connection to Galactic Standard, and one nebulous connection to Albedo.
Personal guess is someone was a fan of Commander Keen, or read Albedo, or both.
The legends book font looks like a cross between heirohlyph style and something else. IE: Some letters are whole words or names like in Egyptian and Mayan cultures and others.
Hope that helps any future delvers into the mysteries of the series.