Sorry, no ingame message telling about destroying "abandoned" state stuff!
One odditiy: If a crew bails its ordnance (vehicle or gun) not in line of sight of any enemy units, then the "abandoned" state vehicle or gun will be completely invisible to the opponent (human or AIP)! Only the crew can be spotted or unspotted normally. That means an abandoned state KV2 in example will stay invisible, despite its size. However, if you move a unit into a hex with abandoned enemy stuff that became invisible due to the mentioned circumstances, you can observe that the moving friendly unit icon will become offsetted from the center of the hex, slightly upward. Normally you know that there is something, either a yet unspotted enemy unit, or....an abandoned/destroyed unit that you just can´t see!
Btw, the info concerning destroying abandoned stuff can be found in the Update.pdf document, concerning V4 changes:
"A unit which has been abandoned, may now be spiked by an enemy unit that spends one turn in
the hex with the abandoned unit and make an experience check. This will destroy the spiked
unit. The unit and leader spiking will receive experience for the kill, although the leader will not
receive a kill credit."