[otrs] ticket number in new mail ticket

hi list I'm trying to add the TicketNumber to the signature or mailbody of a new mail ticket. If opening the new mail ticket screen, the already gets evaluated to "-" as there is no TicketNumber yet. Adding it to SysConfig Ticket::Frontend::AgentTicketEmail###Body leaves it unevaluated. Is it somehow possible to have the ticket number in the signature or mailbody of a new mail ticket? - Thomas