Enhance SUBSCRIPTION_REFERENCE prefix.

coin/settings.py

@@ -239,7 +239,7 @@ MEMBER_MEMBERSHIP_INFO_URL = ''
 
 # Pattern used to display a unique reference for any subscription
 # Helpful for bank wire transfer identification
-SUBSCRIPTION_REFERENCE = 'SUB-{subscription.offer.reference}-{subscription.pk}'
+SUBSCRIPTION_REFERENCE = 'REF-{subscription.offer.reference}-{subscription.pk}'
 
 # Reset session if cookie older than 2h.
 SESSION_COOKIE_AGE = 7200