Tracking offline events is difficult. Be prepared that it will be impossible to track 100% of your offline branding efforts. For example imagine somebody sees your poster, remembers the name, googles your org and lands on your site. They will be considered organic traffic.

The old way was to use different phone numbers for each poster, and measure the number of calls that each poster generated using call tracking. This is the same way that infomercials test markets/times/channels/etc...

Nowadays we use websites but the process is still the same. You can use bitly codes, or multiple domain names to measure which poster drove which traffic, just keep in mind that rarely does a poster convert right away. People riding the subway or driving etc are in a completely different state of mind. You could try and attach a unique incentive to manipulate that (free t-shirt!).

Alternatively you can _infer_ the success of your posters based on what neighborhoods traffic is coming from, how much on mobile, and other analytical cross sections, but you should remain skeptical of the accuracy of this process.

Personally I wouldn't worry about which poster, I would just worry about posters total. If you see traffic increase and keep all other things equal then yay!

Good luck!

The trick with any offline media is to plan some kind of unique value that the person should use to connect with the business, examples would be:
- Custom URL (ex: www.clarityformarketers.com)
- Phone (Ex: 1-888-Marketers)
- Discount Code: use MARKETERS to get 20% of your first call
- SMS a custom CODE to get a discount
- QR Code to receive discount code
etc...

The other then you'll want to do is ask the visitors to your site, or business "How did you hear about us?"

I will say that it's only 40% accurate as most people will think they heard from a friend, but maybe initially got introduced to you via a radio ad, or facebook promotion. It's not accurate, but the easiest of all the options.

Hope that helps - call if you need more
http://clarity.fm/danmartell

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.

Poster #1
Tear-Away: CALL 902-555-5555.
Email: EMAIL funtimes@gmail.com

Poster #2
Tear-Away: CALL 902-555-4444.
Email: EMAIL coolbeans@gmail.com

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.