Type Size and Other Factors:

Type size is important, but remember there are other factors in creating readable type on signage; Typeface selection, Color choice, and Uppercase vs Lowercase. See below for hints regarding these three.

Type Sizing is Critical:

Generally the point of a banner or sign is for humans to easily read it from a given distance. The most important factor in acheiving this is using a large enough type size.
The following chart is a guide to choosing the correct type sizes for your designs.

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Choosing Typefaces:

I know it is a great temptation to use fun and interesting fonts when creating a design. But remember; if the goal is for high visibility from a distance, then lean to the side of restraint and use more plain typefaces. Typefaces without serifs (the the little pointy things on the legs of the letters) are even better.

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Color Choices:

Colors can be the making or breaking of a good design. Without delving into the exciting world of color theory and such, a few pointers are: Avoid things like primary opposites (Red on Blue) or low contrast differences (black on gray). If you steer clear of these mistakes, people could see your banner from the moon. Assuming that your banner was large enough and and you put it on the moon somehow.

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Uppercase vs Lowercase:

A point of much debate within the sign industry is whether UPPERCASE is more ledgible that standard Capitalized-first-letter-with-lowercase-following (eg. "SOME TEXT" vs "Some Text"). The truth is (according to the United States Sign Council). Full uppercase words are between 14% and 17% less readable on signage.
So if you want maximum readability, use standard lowercase words with capitalized first letter.
Of all the readability factors listed on this page - this is probably the most flexible. If you really want to use all-caps, then go for it. Just make the font a little larger. Or dont.

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