There are many of them in Europe and the smaller ones change names quickly.

Turn off adblock and go to finance and forex oriented sites. You will see many ads for them at least in Europe.

A common marketing strategy for them is to offer heavy affiliate comissions and this leads to make-money-with-forex type of affiliate sites. That's another sign.

Bigger ones would be someone like Saxo Bank which started as a bucket shop in 90s and now is medium sized and somewhat legitimate now.

Another sign to be aware is the use of Metatrader software. Up to version 5 now.

I am sure there are turnkey solutions offering a whole bucket-shop as a service.

Even if there are honest bucket-shops you are still betting against the house not against other players in the market. Might as well bet on horses or sports then.

EDIT: nice discussion here on situation in UK: https://www.elitetrader.com/et/threads/is-there-an-actual-ma...