It doesn’t appear on any lists of Dutch road signs I can find, including this government guide. The closest one is the general warning sign, which has an exclamation mark, but that’s definitely not what this is.
Not terribly retired in Spain or France either. More likely to be found on secondary roads, but that’s simply because those are lower-priority for updates in general.
The clue is in the hanging sign behind it: that particular stretch of one-way road is going to change direction soon. The unusual yellow sign is about “high probability of frontal collision if you don’t pay attention to the changed one-way signs”.
I’ve always had this sign in my headcanon as the “prepared to be startled” sign. But yeah at least “!” conveys a general “hey, watch out” message better than a plain “|” .
It actually means NO HORSE DRAWN VEHICLES. That it is a prohibition is conveyed by the red circle, and the picture tells you what it is that’s prohibited. A similar picture in a red triangle means that you should beware of horse-drawn vehicles.