In Thailand, "Seasoning Sauce" most often refers to Golden Mountain Seasoning Sauce or the famous "green cap" sauce. In recipes, it can be used interchangably with Maggi seasoning although the taste between the two is significantly different.
Golden Mountain Seasoning Sauce is composed mainly of fermented soybeans and salt but has a "deeper, somewhat saltier taste" then regular soy sauces. Like Maggi a little goes a long way (just one or two drops makes a big difference).
It is particularly good in spicy stir-fries like Pad Kaprao.