Its the number before 100

They might have used 99 to mean "night night".

I think it means help.

If you include the sentence where you saw it, we'll better be able to tell you what definition you're dealing with.

I'm obviously too old to know what 马先生 is suggesting about the 'unsuitable' meaning of '99', but I do know about the ice cream. It's vanilla ice cream in a cornet, with a stick of flakey chocolate.