What does "brokers protected" mean when on a for sale sign on a commercial building?

I've never heard that term before and I've seen alot of home deals go
through.  After some searching, I think it means that the broker
(usually the mortgage broker but possibly the real estate broker, or
both depending on how the maker of the sign intended it) can not be
cut out of the deal.  Without "brokers protected", there are ways to
get information or services out of either party and then cut them out
of the deal (not pay them commission) before the final signing of the
contract.

I expect that means that the broker has an exclusive contract with the
owner, one which also says that anyone trying to deal directly with
the owner will have to be referred to the broker and pay commission. 
Fair enough.  It saves the owner from being pestered by calls from
potential buyers and from other brokers, and a broker  may get a
better price for the owner than he would from his own negotiating.
When I was looking for a house, I found one place offered in the same
newspaper by three realtors.