In plain English
This road is closed to you from this direction — usually because traffic is coming the other way and there's no room for two stories at once.
Where you'll see it
At the exit end of one-way streets, bus gates and slip roads — anywhere driving in would put you head-on with traffic.
The common trap
Confusing it with "no through road" (blue with a white-and-red T). No entry bans you now; no through road just tells you there's no exit at the other end.
Memory anchor
A red circle with a white bar across it — like a barrier arm down. The road is saying "not this way."
Quick check