There are many ways and alot of them have been mentioned above but I just have to add using influencers to hype your project on YouTube, TikTok and twitter. Alot of users still listen to those guys and will buy anything they talk about. Getting them to hype your project will give the project some publicity and if your project has something different to offer from the rest of the projects in the market, you'll get yourself some loyal investors and you can start building from there. I won't recommend bounty right now because they don't bring in investors anymore as they use to since most participants uses fake account that don't get any genuine engagement but just bots. Their comments on the social media profile of projects they advertise looks spam like and might likely chase away potential investors that visit the social platforms instead of attracting them.
Signature won't be the best option either because the exposure is limited to the forum. If your project is a gambling, mixer focused project that's when you'll get a lot of interest from the forum but anything altcoins should be taken to platforms that you'll get more results for the expenses you're going to make. You can also try media platforms that specialized in crypto related news as they get alot of engagement from cryptocurrency users. Getting an ad slots on this platforms will introduce your project to alot of crypto users.