I do not if it is against any rules, but I think it is bad form. I would not go into someone's restaurant and pass out flyers for my restaurant.
You might try talking to owners of similar channels and see about a collab? That you both get advertised to each others viewers.
I would say it's against YT policy if you keep on commenting on other channels about subbing to your channel. People can report your comment for spam advertising.One of the strategy to grow your channel is to get more subscribers. Is it wrong or against Youtube policy to comment on other channel videos and ask people to subscribe to your channel?
It's definitely distasteful and rude to go onto other Youtuber's creations to advertise your own channel. Instead maybe do this, write a comment about the video which shows that you watched it and care about the content, then sign off "from a fellow Youtube creator". That way, you're taking part in the conversation, as well as low-key advertising yourself that you're also a creator.
Basically like all have said it's a no no. What i have learnt is to be part of a regular commentator on a popular channel around my niche. Over time as I make lovely comments, people will be curious to find out more about me. In a subtle way like someone said, I refer to my channel like ' oh dear, what you said was on point, I was making the same point in my video last week'. Believe me people are curious and will want to find out more about you. I have had some creators I admire check out my channel just because of positive feedback I made. I hate when people come on my channel to start their sub to sub, I the comments down. Subscriber will come as we keep improving on what we do.One of the strategy to grow your channel is to get more subscribers. Is it wrong or against Youtube policy to comment on other channel videos and ask people to subscribe to your channel?
IΓÇÖm the same, anything like that in my comments section will get removed, but not until IΓÇÖve taken a screen shot of it.When I've seen links like that in my comments I delete them and block the user if they do it again.