What I want to do is to mark a calendar with holiday's (by using an "H") the
below equation works - is there a better way to do this?

I have the months starting in row 11 thru row 22 and the days of the month
starting in column b thru af. This array formula is in every cell of the
year as defined above.

{=IF(OR(DATE($AM$10,Brad!$AM11,Brad!B$10)=Holidays !$F$5:$F$12),"H","")}