The other end of the road will see a "No Entry" sign (red disc with a white horizontal bar) and any side street will get a "mandatory direction" sign (a blue disc with a with circle and a white arrow) that shows which direction is mandatory or a "no turning" sign showing which direction is prohibited. The square blue sign with an arrow is an indication that someone else has mandatory or prohibition signs.

For example here: https://maps.app.goo.gl/PwAYqUffz6uPLVZW6 you can see a "no right turn", a "one-way traffic" sign, and a "no entry" sign (all saying "except bikes"). The "one-way traffic" is definitely informative, it would be a disc otherwise.

Now, I'm used to France, Belgium and the UK but looking at this chart: https://en.wikipedia.org/wiki/Comparison_of_European_road_si...

it seems like it's less universal than I thought. Using just a rectangle with an arrow when coming from a side street rather than a circle makes no sense to me unless there are also no entry/no right turn/mandatory left turn signs as well.

The one-way traffic sign does fit in, but most commonly you see it in situations where it's actually just informational, like the entrance of a road. In this case it doesn't limit you in any way, it's not like you have to enter that road. You will see a no entry sign on the other side of the intersection anyway, which does limit you. But it does inform you that you shouldn't expect oncoming traffic.

The horizontal one-way road sign is less common, and is often used in T-junctions. There it arguably does double duty.