If Boeing would one day make the man machine interface in the 737 compliant to the rules, currently one of the exemptions, and install EICAS, such a pictogram would be a simple thing.
Boeing got that exemption with the argument, that it would be expensive to comply with the rules.
I seriously doubt a pictogram of the trim moving would be of any more help identifying the problem, than the two trim wheels spinning away right next to your knees. Something more along the lines of a large, red "MCAS ACTIVE" message on the PFD might be more helpful.
I wouldn't get so wound up about the lack of EICAS/ECAM on the 737, it's nice to have all the cautions and warnings centralized, but you can get along just fine without it, and without a specific warning that the MCAS was working, it wouldn't have made any difference in either of these accidents.
The trim wheels work "all the time" in bursts whenever the speed trim system is active. This is why no 737 pilot will be concerned or even be "alarmed" to see and hear the trim wheels spinning. This is routine.
Normal STS bursts are quite different from the wheels zipping away for 10 seconds straight while the column is getting heavy requiring extreme effort to keep the attitude normal.
My impression is that something psychological. It is relatively easy to react to onset of something, especially unexpected onset. But onset of trim is routine. Recognizing that the pattern is different, it requires conscious attention to that particular process - and attention was focused on other issues as there are quite a few.
I'd argue that anyone who has flown the 737 for any length of time, should have developed awareness of what the trim is doing, all the time. Every time the trim runs for more than a few seconds, without one of us touching the trim switch, I automatically start paying attention to what it's doing. Always have, on every airplane I've flown.
During my last recurrent simulator, even when we were just about upside down during the upsets, or fully stalled, with the sim shaking so hard we could hardly read the instruments, while descending 10,000 FPM, both of us could have told you when the trim was running.
True, but stall warning, stick shaker going off, cockpit lighting up like Christmas tree is not normal. Somewhat unusual STS behaviour would not be unexpected in such situations?
Why would STS stand out as the lethal killer when there is a lot of things going on at the same time?
At the same time, electric trimming worked normally, indicating to the crew that there was no (classic) trim runaway.
This phrase drives me nuts. There was a master caution, and a couple of other system caution lights presented, a very far cry from "lit up like a Christmas tree".