High-quality pictures of signs are great raw material for a presentation. They stand out by themselves, people are used to take a moment to read them and they could add some humor to your story:
  • Typos, or unusual text as an ice breaker for your audience
  • A correct message that is put out of context in a funny way in your presentation
The downside, they are very hard to find, but with a bit of creativity you can re-create them either by using a blank sign from a stock photography site, use a generator like AddLetters, or - even better - creating one of your own using PowerPoint shapes.
Here is a diffrent take on the credit crunch found on Noisy Decent Graphics: