Editable PDF File

I have a client who needs to edit some text on a PDF file I have created. Never done thise before so I am learning on the job. The slight difficulty I had was the price has 2 size £ is larger than pence.

Managed it and sent it over to them to test. the issue is, when they change the price a small '+' appears bottom right of the editing box, this also prints.  See attached.

What is the + and how do I remove it?

Thanks