Those of us who are slower cyclists may spend much of the ride with just our team. In one case, similar small group(s) missed a turn and we, following them, went off route, too. Since the signs were “invisible” from the opposite direction, it took a while to find the route again. It was clear weather with full sunlight at the time, and one to two dozen riders were involved. When tired & hot, pedaling with head down, it’s also easy to not look up at the right time — signs are higher than the pavement & riders. We use everything: signs, maps, GPS, other riders, residents’ advice, etc.
Perhaps (very fat) permanent magic marker pens could be used to hand draw an arrow on the back of turn signs when they’re being posted — inexpensive and easy.
Maybe on the front side, too. We also found the current graphics difficult to read from a bike.