From Handbook of Nature-Study by Anna Botsford Comstock, 1911.

From The Lewis Story Method of Teaching Reading and Spelling Manual, illustrated by Bess Bruce Cleaveland, 1919.

Here's some sort of thing in an ornate capital P, from an 1862 issue of Fun magazine.

From Judy, Or The London Serio-Comic Journal, 1876.

Here's who is minding your P's while you're minding your Q's.  From St. Nicholas magazine, 1900.  And note that Mr. Punch graces one of those rare drop capitals sporting a quotation mark.

Here's someone minding his P's, if not technically his P's and Q's.  From Songs of Singularity or Lays for the Eccentric by the London Hermit, Walter Parke, 1875.

The Shakespeare Papers dedicated an entire issue to one-letter words, and here's one of the pages we contributed.  See our One-Letter Words: A Dictionary.