8.23 Special observation powers

[Blackcloud6]

So you are saying making the tank spotted is at the whim of the active player?

I would say it is immediately spotted when it moves into the spotting range of the enemy recon unit. marking it as such is immaterial as the marker is merely a reminder.  So, the unit is not spotted by the whim of the enemy player, it is spotted when the rules say it is spotted which is when it enters spotting range of any unit.