Caught Writing In My Book

"odd wasn't it, that the crispest memories were of aberrations." (Mirror, Mirror, Gregory Maguire, page 163.)
I was caught off guard by how true that is - so I took out my pen and underlined the sentence - to make sure I would remember it or at least could find it again.

A woman sitting next to me on the couch, also waiting to have her hair cut, saw me do it.

She waited a few minutes and then said, "you wrote in your book."

I was startled. "yes, I did. But, its ok."

She looked puzzled so I blundered on. " I own the book."

That was not enough. She did not look either satisfied or forgiving. She looked at me - like a librarian - - so I added, "I mean its not a library book."

"oh."

I knew she would tell people.