There are some good ideas in this thread.
"So I am reading your 2018 2019 forum thread, and it occurred to me, when I am out and about, I see somebody with gator gear, car tag, etc, if I have a chance I talk a little gator talk with them then mention to them to check out this site."
Carib is right. You can do an organic grass roots campaign.
Assign every member a referral code as Carib suggested. Members could be given a URL that would take people directly to a signup page and would credit the referring member with the registration. And add a box to the signup page for referral codes. QR codes might be useful too, for potential members that are more smart phone oriented rather than PC oriented.
Incentive:
Oxbucks for referring new members. And set up a process to make this easy to track.
Contest:
A contest for referring new members. You could do it yearly, but people might lose interest if they aren't in contention early on. So you could make it semiannual or quarterly. Maybe have a regular season to get into a bracket style playoff. Then the top referrers can shoot it out head to head during the playoff rounds.
That would have interesting implications as top performers would probably hold back once they locked down a playoff spot, but if it gins up more interest in the campaign, then why not? The prize would be bragging rights on the board, and an Oxbucks prize. And not having to streak naked with the GCMB log painted on their arse. Maybe a trophy (or virtual trophy) and some GCMB swag.
GatorJ has a good point about demographics. We probably fit into a pretty predictable segment. If you spend real money on marketing, that's going to be important. If you can find the right mail list, you can do a snail mail or email campaign. ChiefGator's targeted mail list is a good idea. How you execute that is going to depend on budget and goals.
I agree that the "share" button idea probably doesn't resonate with our demographic, but if you can get something out there in those channels for little or no cost then it wouldn't hurt.