Rather than having to spend countless of hours to try recruit some good members. A clan could simply make an ad or something that show's regularly in another user's page.

You know that you can pay tc to make a banner that shows on the top of the forum?

That option is not available for quite some time now.

On the other hand I like the suggestion of ads for clan recruitment, will be easier for newer clans to gather up people in the beggining

Do you have any suggestions on how this would be done? It seems a little out there to me to add our own forum to an ad bar.

I think the banners on top of the page should be used for official events and important announcements only. There are normally not many more than 5 banners in circulations, and it can already take a while before you see a specific ad, as the one showing up is totally random.
Adding like 20 other of them for people that need recruitment would make some of the more important things almost impossible to see.

And any other sort of ad you're wanting implemented would ruin the forum experience for lots of people, as this forum has been ad free for years, and people like to keep it that way.

Well maybe it doesn't have to be on the forum. I was thinking of basiclly having a little bar on the top of the client that has which clans are recruiting. E.g. Say [WAPOW] (Oh) and [Obey] were actively recruiting in game or out. The bar would then display the clan's desired recruitment message and those messages would change to the other clan's messages after a certain period of time. Of course if this is implemented there would be the option to disable it.
Anyway that's just my opinion of how this should be done if Clan ads should be implemented.
Sorry I don't have any visuals I'm posting this all from my phone but you get the idea.

i can only recall seeing 2 non-official banners in the time this was available

it hardly affects the official ones

Just because you only saw two unofficial banners doesn't mean there won't be more than two at any given time if unofficial banners became a thing again, so just because you've only seen two doesn't mean anything. Anyway my real reason for posting here again...
I was thinking why not allow unofficial banners in again? The only main problem I can think of with re-allowing unofficial banners is that the official ones might never been seen ever again which is a really big problem thankfully I've come up with some solutions to that problem. (Probably)
Solutions:
1. Set up a percentage system for the showing of banners. E.g. Official banners will get shown 75% of the time while Unofficial banners will only get shown 25% of the time.
2. Have a limit on how many unofficial banners there can be.

Anyway, these are just some random ideas I came up with on the fly.

or you could like
put the clan link in your sig
and post on the forum

Not everyone will see your post's signature. Besides let's not forget that not everyone tends to look for a clan. Which makes the chances of someone joining the clan even rarer than of a PM or something.
Just my thought.