These are my special invitations. 
...
They have been placed into this separate tray
so as not to be mixed with other mail.
...
They have been
"hand cancelled"
to keep them clean and neat. 
...
Please do not place them through
the cancellation machines again.
...
If these are oversized, 
please give them special attention 
and keep them from the
cancellation machine used for "flats." 
...
This mailing is very important to me...
Your efforts to keep these envelopes
as clean as possible will be appreciated.
...
Thank you for your kind assistance!
 
 

 courtesy of "JB Ink. Invitations"