As far as I know, there isn't a variable, but you can make the (dim)style annotative when you create it:
(command ".-style" "STANDARD" "ISOCP" "A" "y" "n" "" "1.0" "0.0" "N" "N")
(if (tblsearch "DIMSTYLE" name)
(command ".-dimstyle" "ANnotative" "yes" name "YES" "SAVE" name "YES")
(command ".-dimstyle" "ANnotative" "yes" name "SAVE" name "YES")
)