The Twitter CEO posted a link Saturday to a site called Valuables By Cent, where folks can buy/sell authenticated tweets with their autograph. Jack, too, was putting a tweet up for auction ... his own from 2006, when he wrote ... "just setting up my twttr." It's the tweet that kicked off every other tweet thereafter, so it's historic -- and the bids bear that out.

At the moment, the highest offer for ownership of his tweet sits at $2.5 MILLION -- courtesy of Bridge Oracle CEO Sina Estavi ... who's been in a bidding war of sorts with another tech entrepreneur in the crypto world, Justin Sun, who was upping his price exponentially.

Sun seems to have started at $500k, and then incrementally upped it to $2 mil, but it looks like Estavi swooped in with $500k more ... there haven't been any further offers since. Per Cent's rules, if anyone wants to outbid Estavi -- they'll have to throw down $2.75 million.

If Jack's tweet sells at this amount ... it would follow suit with tons of other online transactions that have flown off virtual shelves at eye-popping values among influencers, artists and sports leagues, like the NBA ... which has been dabbling in this for a couple of years.

For instance, you can actually buy NBA highlight reels and awesome moments from games through NBA Top Shot ... which tends to sell these "moments" in packs. Some of the more elite highlights -- like some of LeBron's and Zion's -- have sold for upwards of $200k!

Might sound nutty, but selling digital assets like this is a thing ... which they call NFTs (non-fungible tokens). They're essentially one-of-a-kind collector's items that are recorded on a blockchain network -- the same system that supports and tracks crypto -- and which aren't interchangeable, unlike something like Bitcoin, which can be swapped back and forth.