The above answers were great to address the problem of which 'mediums' to track registrations. Use the below framework to help track the 'success' of the posters.
First off, there are 4 key actions you your want target audience to take:
a. STOP (walking)
b. Read poster
c. Register (see below)
d. Attend Event
Before you get too far with a website, you need to make sure the transition from A to B is strong. So create 2 posters. One with fancy graphics; the other just plain block writing. Each poster should use different 'tear-aways' and emails.
Tear-Away: CALL 902-555-5555.
Email: EMAIL email@example.com
Tear-Away: CALL 902-555-4444.
Email: EMAIL firstname.lastname@example.org
Than put both posters up in your highest traffic area. Find a seat at least 20 ft away. For the next 30-60 minutes, watch how many people stop to read each poster. See which version compels more STOPS.
I guarantee one version will way outperform the other for STOPS and REGISTRATIONS. Track for the next 2 weeks.
This method will allow you optimize your posters. Than you can figure out if they are a good 'medium' to attract attendees going forward.
If you want to know more, lets set up a call.