I came across the following example of permitted signal operations on my travels and hadn't seen the sign Let Op with the arrows showing permitted operation of the signal.
The yield signs posted on the traffic signal poles are mounted low and are helpful for those that may be waiting at the signal and aren't familiar with the movement. I would assume that this isn't a very busy crossing and it serves as a reminder for those that are travelling it on a daily basis. If there was a problem, I am assuming that the protected operations would be a retrofit, but since the traffic is so low the risk is unlikely to be of major concern related to safety.
In the U.S., we don't often like to add a supplemental sign that explains the traffic signal control. the legibility of those signs is of a concern especially at higher speeds.
One of the principles we learned from the opening day presentations is that the Dutch place safety as the highest priority. One of the principles of this is that they don't want to have turning traffic at 70 km/hr because of the risk of a crash, so they don't have traffic signals at high speed intersections. As an engineer responsible of signal timing, they have it right. The inherent nature of speed limits at traffic signals, an argument could be made that the Dutch experience of setting lower speeds at signalized intersections is important for pedestrian and bicycle movement and if the higher speed is desirable separation of modes should be given serious consideration.
UPDATE: In class today, we were discussing what the difference between permitted and protected signal operation is and Peter called on one of the Northeastern students to give an answer. When he couldn't articulate the difference, he called on a student that had taken the "Traffic Engineering" class. I had to blurt in at that moment because 20 and 21 year old students that have been driving for 4 to 5 years, should be able to answer this question. This makes me wonder how permitted operation works as well as it does. Perhaps it is just such an obvious question that the students weren't able to articulate it because it is like asking how do you breathe?