It was even called OICQ (OpenICQ) when they first started, even though there was nothing "open" about their service.
it also uses a penguin as the mascot...
ICQ is kind of an example of the numbers-website phenomenon in English: the letters themselves are meaningless, but when pronounced sound like "I seek you" (compare to the Alibaba example in the linked article).
I still know my ICQ number by heart, but cannot remember my own land line and only recently managed to memorize my (company) mobile number.