To be fair, having driven through it north to south twice in two days, the thing is terribly marked. You go at 70 mph all the way to the services junction, where the limit drops to 50, if you have any lorry traffic in lane 1 (and there always is), you don't see any of the temporary boards on the bridge, on the way down speed limit is reduced to 40 mph, you see toll booths down below, but that section is closed/concreted off, with temporary multi lane detour/diversion around the booths arranged with so much furniture, signage and flashing elements that even if there was an info board, you wouldn't see it. Immediately past the diversion, the moment your wheels touch A282, it's 60mph limit, lorries on the left hand side and within 10 yards that's the last time you see low hanging "Dart Charge, find us online" board.
I know the charge is there, I heard about changes on LBC in November, I know when it operates, I have an account, I'm fine, I'm safe. But if I didn't know, I honestly wouldn't know what exactly the setup was. It looked like a free temporary crossing, the boards at 70mph looked like some sort of London Congestion Charge (red signage with C in the middle) was in operation somewhere nearby between 7 and 10 am (continental traffic would expect EU normalised 7:00-22:00 on boards btw). I wouldn't expect any foreigner to have online access and know what to find, how to find it, since no urls are provided anywhere etc. I think they screwed the pooch with the arrangement and signage and to be perfectly honest, I kind of expect the arrangement to be screwed on purpose just to extract even more money.