The old chant goes 'mirror, signal, manoeuvre' but simply seeing an indicator flashing is neither guarantee they've checked the mirrors or are fully aware of what's around them.
I drive a 26 tonner and sometimes a 7.5 full time and it gives you a different perspective on driving and other drivers in particular. You cannot take anything other drivers signal or don't signal as any guarantee of their intention or that they are aware of anyone around them at that moment.Most drivers are more concerned with getting where they are going, to cutting into or changing lanes at the lastest possible opportunity so they can get ahead of others.Few of them have any conception of how much room or road a fully loaded 26 tonner requires whether it's at junctions, roundabouts, changing lanes or how long it takes to break. Neither do they consider your blindspots and happily sit on your back doors never thinking you have no chance of seeing they are their if tailing you before blasting out to overtake with no prior warning, cutting in tights before lanea merge.
You're big, slow and in their way that's all they worry about but you have to know what is all around you at ALL times. I may have running bars down each side so cyclists don't go under but it doesn't stop them thinking they can blast up the offside dangerously difficult to see and to be perfectly honest if one sped up the side of me as I turn left all of a sudden I would probably not even feel them as the rear wheels made pate of them, it would be less of a bump than a decent pothole.
It's no use any driver saying another driver didn't signal off a roundabout or on. Position is isn't a guarantee of what they intend either because it takes two or more to collide.You almost always have to expect other vehicles to do something stupid despite what it seems they are doing you can't assume anything because standard of driving over here is useless as a whole and it seems like 50% at least are quite happy to take some serious chances to get where they are going a few minutes quicker if they can,the amount of times cars will sit at a junction until rhs last seconds before pulling out right ahead of me and get pissed off at me for their hesitation.
If I hit anyone else on the road I will kill them 99 times out of 100 in a 26 or 7.5 so it's as much down to me anticipate what other road users might do.