I think signatures are great, and I'm glad you included them. Some feedback on the current implementation...
1) Creating a signature policy might be a high priority to stop abuse before it happens.
2) Right now there is no separation between the post and the signature. Just one line break, so they run together. There should be a better divider to indicate where the signature starts. I used some "====" to create my own divider, but that counts toward my 2-line limit (see #4 below).
3) Maybe allow HTML links? (I tried it but it was stripped out). My vote would be yes, but if not, maybe mention it.
4) 2 lines only? I created a 3 line signature but it got truncated. Maybe mention the limits.
5) Depending on whether and how you choose to implement a connection to Strava profiles, you could make an easy option to link to Strava profile in the signature if it's not already displayed elsewhere.