here is one way

TOTEXT(TODAY,"dd")+
(if month(today)=1 then 'A' else
if month(today)=2 then 'B' else
if month(today)=1 then 'C' else
if month(today)=4 then 'D' else
if month(today)=5 then 'E' else
if month(today)=6 then 'F' else
if month(today)=7 then 'G' else
if month(today)=8 then 'H' else
if month(today)=9 then 'I' else
if month(today)=10 then 'J' else
if month(today)=11 then 'K' else
if month(today)=12 then 'L')
+ right(totext(today,"yy"),1)