Retired Documentation: You are using the documentation for version 1.7.3 which was retired in 2013. Go here for the latest version documentation or check here for your available upgrades to the latest version.
The Stand-Alone Entry Form with high ASCII characters
Entries made via a Stand-Alone Entry Form have missing characters or show question marks or similar symbols instead of the expected characters.
Troubleshooting
Characters that fall outside of the set of 7-bit ASCII, like accented characters, typographical quotes, etc. must be encoded properly. What's more, this encoding needs to be declared correctly in your document.
While ExpressionEngine handles the complexity of this declaration for the control panel, all templates, including all Stand-Alone Entry Forms, should include a line like the following in the <head> section of your document:
<meta http-equiv="Content-Type" content="text/html; charset={charset}" />
Unless you have good reason not to, it is recommended to use utf-8 and turn off "Automatically Convert High ASCII Text to Entities" in your Global Weblog Preferences.