These are small letter-size posters that, when lined up, spell out CUPS. Each poster specifies what each letter stands for (Capitalization, Usage, Punctuation, Spelling). I remind my kids to always check their CUPS when writing. When proofreading, I'll indicate the number of errors of each type (CUPS), so that students know how many to look for.
I've also made ARMS posters to go along with these: http://www.teacherspayteachers.com/Product/ARMS-Posters-Add-Remove-Move-Substitute-858394