We flew with Thomas Cook in April.
They have just sent me an nice "Welcome Home" email.
They have also offered me £10 off all return flights booked in next six months.
I have checked and if I type WELCOME in the promo box I do get £10.00 knocked off the final price.
It was probably meant to be secret so don't tell anyone.
(The promo box doesn't appear until you get to the very last window before booking - after you have entered all your details)