And furthermore, maybe it shouldn't be COMPLETTELY and UTTERLY irrevocable. I'll do my best to summarize the conversation that prompted this idea, but you should probably read the full conversation in case I missed something in my attempt to summarize:
It came to our attention that the current implementation of truenames/player-reference-foci can be really frustrating and disheartening for some players, particularly with as easy as it is to miss the warning in the patchouli book (it only appears in one chapter). As someone put it, "I committed a mistake that no amount of further gameplay can undo" and they later said "even if I wanted to give someone my trust I would also have wanted a way to retract that trust later" to which Sam commented "Yeah,, the truename system is kinda wack[sic]".
The conversation has thus far yielded a few observations:

• For one, would be great if there were a warning, unique from any sort of mishap, right in your chat the first time you write your reference to a writable item.
  As for what the warning should say, object-Object suggested the following flavorful warning text that could appear in chat, ideally with emphasis and other formatting to set it apart from mishaps:

  "I've heard legends of the fae stealing souls. I should be very careful who I give this to, lest it come back to haunt me for eternity."

• Secondly, it would be really nice if there were a way to give someone access to your player reference, but revoke or limit it somehow. One idea I remember seeing discussed in the past is single-use foci, sort of an inverse Thought-Knot, which can only be read one time but can be written to repeatedly, possibly even after being read. We also did at least a little brainstorming about making it possible-but-expensive to invalidate ALL existing true names (even those inside casting items and circle impetuses). like there could an integer that sits beside the UUID in a truename. Before you do anything with the UUID, you check the integer to see if it still matches an integer stored in a global table (hash map). If it doesn't match, these trucks all fail and the reference becomes null.

To add to what has already been said, a special (and ominous) sound cue when writing your true name to somewhere would really help to:

1. Bring attention to the warning message in chat
2. Make it obvious you're not just writing a regular old iota to the focus
3. Make it hard to get away with making a trinket that writes someone's true name down without them knowing (although this isn't even intended behavior so I don't know how relevant that is)

Truename stealing is not pvp, it's tech support scam simulator

while I'm not sure if truename stealers are necessarily unintended on the whole, I do think any PvP-related elements of the mod should do their best to make it clear someone is could be PvPing with you, and in general you should be able to opt out without leaving the server unless the admin has explicitly allowed it somehow (beyond just enabling /pvp, since this is kind of another level of difficulty?). The more aggressive truename stealers I know of tend to dump your inventory and force a bunch of foci into it, so they are rather obvious, but something like what determied tried on me early on (at least, I think he was trying) where someone hands you a spellbook and asks you to test a trinket for them... might not be obvious enough.
either way, I definitely think an ominous sound effect whenever your "soul" gets bound to something permanent besides your person makes sense. kind of thinking a sound along the lines of Thaumcraft 4's warp SFX? Maybe not.