I think the c/n (= also Thai number?) is painted on the bottom of the nose (below the radar nose).
Maybe you can read this on one of your original pictures?
Log 28-10-2016 (because of fog no flying) D-HTSC EC135 cn 0832 (primer, in hangar) D-HECR H135 "853" Australia full c/s (towed) ?? H135 "855?" Australia full c/s (in H135-flight hangar) D-HECL H135 white c/s (towed) ?? H135 primer (outside afternoon) ?? H145M cn 20016 (primer, in...