I think seafood sauce is Marie Rose sauce - it's what you get in a prawn cocktail (oooer on a football site, Roy Keane will be fuming). They're all based off a tomato sauce and mayo base, but the others add other spicings and ingredients to it to mix it up.
Marie Rose is literally tomato sauce and mayo. Thousand Island adds in stuff like vinegar, Worcester Sauce, mustard etc to give it a bit more tang, it tends to be quite thin too (it's a salad dressing at the end of the day).
EDIT - I'd put money on Hellmans Burger Sauce being similar to these 2 but not exactly the same, but probably along the same lines - tomato sauce, mayo, and some spicier racier ingredients to give it some oomph. You could probably knock up your own a few minutes with some stuff from the cupboard
Thats it and it was amazing.
Im going to experiment and i will report my findings.
Ketchup + mayo + paprika = ???