I don't think there is a tag for that but you could use a conditional statement.
Place a TEXT element where you want the A/P to be and in the text field type the following:
This reads as, if the text that the tag #Da# returns equals "AM" then "A" else "P".
Note that you must type the conditional statement exactly as I have above; no spaces anywhere in the text, no brackets around the test part of the expression,no brackets around the outside of the whole expression and no quotes around the AM text.
There is a short section on conditional statements in the documentation that will explain this better.
I hope that helps.