since we have harmonized the payment terms, we strictly split between payment term and payment method.
As "T/T" seems to be a payment method, we have to avoid this in the description of the payment term.
There's a special field as well in the customer master (tab accounting) and in the sales order (header+item) called "payment method".
In other SCs where there's a legal requirement to show the payment method on the printouts, this field has been added in the print. So that the payment method and payment term is printed together.
I forward this ticket to my colleagues here in Germany resp. for further analysis and information.
Beside this I had a look if there are other payment terms which are close to what you want as description:
H922 - 30% downpayment and balance against delivery