I can't see why it would be illegal unless gambling advertising was illegal in your home country, so I'd search for that.
Agreed, if any at all then the gambling sites would be the problematic ones. But I am not sure in how far a ban on gambling in a specific country can be legally applied to advertising for gambling in the internet. I have heard of gambling being banned or at least heavily regulated and those bans affecting the hosting of and the parttaking in gambling equally (meaning you are neither allowed to host a gamble nor to take part in it when gambling is banned in your legal area) while regulation mostly aims at the hosting side needing them to adhere to certain rules and being licensed by the authorities.
But laws specifically handling the advertising of gambling services? Do they even exist anywhere? Never heard of anything like that.
The thing is: If your gambling service is illegal in a certain country you should be taking precautions to avoid your service being used there or you can get in trouble, that is why online trading card games that sell cardpacks only for real money for instance exclude so many areas from taking part in their tournaments with entry fee in which you can win packs (because if you can win goods [even virtual] that have a monetary value and there is a fee to enter it is considered gambling and thus the TCG hosters exclude any area in which gambling is banned or in which they have no proper license to host gambling). At the same time the advertising for the tournaments is available anywhere.
