Readability is crucial in the sign market. A significant factor in the readability of a sign is the height of its letters. In general, the determination of letter height depends upon the background space. For a viewer 100 feet away from a sign, the minimum readable letter size is 3 inches, and the maximum impact size is 10 inches. If the view is in a passing vehicle or if the sign is printed on fabric that flutters, letters should be even taller.
Avoid decorative typefaces with a lot of contrast in stroke weight. Very thin typefaces fade into the background, and thick faces fill in at a distance. Typestyles with even stroke weights like Helvetica Bold and Clarendon Bold are ideal for signs.
Use normal or loose letter spacing and line spacing, especially on larger signs. Loose letter spacing guarantees that letters won't run together, especially when the sign is viewed at an angle. Signs that contain two or more lines of copy should have a leading (space between lines) of one-half the font's capital letter height to make the sign easy to read. If you must stack lines, three is the limit.
Type in all capital letters is difficult to read, especially with many lines of type. If you must use all capitals, use large and small caps to help the viewer's eye progress through your message.
Significant contrast between colors is essential on your sign. There must be an adequate difference in tone, not just color.
Tie your signage into your overall identity system. If your logo translates well into signage, use it. Try to pick up a typeface or color from the logo.