From OpenStreetMap Wiki
Road signs in Belgium (F99a and F99b)
Hello. You reverted my changes on Road signs in Belgium for road signs F99a and F99b. I think this revert is not relevant.
- You deleted the tag motor_vehicle=private. The access to the roads marked by these signs are restricted for motor vehicles, so it is necessary to indicate it, either with access=* or with motor_vehicle=* (I think motor_vehicle=* is better, because in the Standard tile layer, if you use access=private or access=destination, the road will appear as a private road, even if there are other access tags for foot, bikes, horses...)
- This is less important, but I do not think it is correct to tag all the roads with these sign with the "designated" value for all concerned transport modes. Please note that F99a with the pedestrian, the bicycle and the horse can be found on forest tracks that are not suitable at all for most bicycles (only mountain bikes can drive them safely). (For example this track has this sign ; at one point you have to cross a stream at a ford, which would not be easy with a classic road bike.) So, I think in some cases, the designated value can be used (for example, when the concerned road has the highway=cycleway tag), but not on all the road with F99a sign.