I think the older generations in particular find business cards useful, so I would make them. I made some music business cards a few months back, and I recently decided to print a new set with the following at the bottom:
YouTube: URL
or search for 'channel name' on YouTube
Business cards can be super cheap - I bought some silvery shimmery metallic cardstalk from an office supply store and used my old black ink printer to make simple, but clean-looking business cards. There are lots of business card templates online, and Microsoft Word even has a few built-in templates.
If you are ever in a situation where someone wants to know what you do, or is interested in what you have to say, I think it's great to have a few in your wallet ready to go! I would include other information on them besides just your channel link - maybe even an inspiring quote. I put an email and contact number on mine, but I'm also trying to creep into the music world and would love to play at local venues and such.. : )
I'm hesitant about using the word "subscribe" on them. It's what YouTube calls it, so it may be necessary, but I've noticed that older folks tend to assume "subscribing" means they will need to pay money for a service. But..I'd be happy if they just watched a few videos and not necessarily subscribed, so I've left the word off for now.
I'm new to all of this, so I've yet to really see if it makes much of a difference, but I don't think they can hurt!