Great question Simon07. HumanArrow had a similar question so you may want to check out that response as well!
Great question. The answer is both are effective but in your particular instance the answer lies in the demographics and preferences of your audience. There are many variables that affect a channel's performance. You need to ask yourself a few questions. Who am I targeting? Are they web savvy? Do they prefer to have a hard copy to read at their leisure? Are you mailing to existing customers or prospects? If they have opted in to an e-Newsletter via email or a web site, they are likely to prefer the virtual version over paper. We do know that on average people spend more time with direct mail newsletters than eNewsletters. Many of our clients provide an integrated approach - they offer both a direct mail and email version of their newsletters.
Is the chalk board working? There are other types of signage that would allow for flexibility. Restaurants typically use the signs with movable letters. Check out displays2go.
Have you looked into digital printing as well? You could investigate building a template and posting/printing specials each week. The cost of digital printing now makes these one-offs affordable.
And the most effective programs use an integrated approach, with direct mail and email. Bottom line, look at what gives you the most "bang for your buck" by analyzing your cost per lead and cost per sale.
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