there are multiple steps to permit the "subscribe" icon to appear. Ensure Access to Subscriptions and Data-Driven Alerts One that I don't see within the link is that you need to have at least 1 active subscription schedule defined. Do you have one setup yet?
Jeff hit the point I guess. The most obscure cause is that there isn't any active subscription schedule.
I was puzzled by this issue for along time. Even after a server upgrade, this issue still existed.
Then I found the solution mentioned in an earlier thread.
Just documented it here