The immediate reference is to SVB and friends, presumably.

By GAAP reporting rules they were nicely solvent, because their bonds were to be "held to maturity", hence not marked to market.
At booked value they looked like they were worth a lot.

But when a bank run starts, NOTHING is really held to maturity--anything might need to be sold, so they were really available for sale.
As soon as they are (correctly) categorized that way on the books, they get pegged at mark-to-market prices instead of historical cost.
SVB's balance sheet was (ahem) not sufficient in this suddenly necessary approach.

The meaning I take from the two signs at the meeting:
I presume Berkshire is going to hold onto Charlie until he reaches maturity.
Warren, on the other hand, can apparently be shipped off to the highest bidder at any time.

Jim