Not always possible. Sometimes I have to step out while wife is sleeping. No way to flip the latch. Invariably, those are the occasions when housekeeping ignores the DND sign.

As for OP, you only have a compensable gripe if you ended up with a lower category room than what you booked. Otherwise, all that happened was an extra trip to the front desk. I wouldn't ask for anything for that... I suppose if it was a really long walk or a long wait then maybe ask for a free drink or something. Can't see it being worth more than that.