"Authority or permission to do or carry on same trade or business which would otherwise be unlawful".

L'espressione completa è:

"Trade, business or calling license"

It.:

"Licenza per l'esercizio di un commercio, una professione od un'attività".

Nel tuo contest; " Per quanto riguarda la vendita di tali prodotti, e' necessario essere in possesso di una "licenza di vendita per i prodotti della sicurezza" rilasciata dall'ufficio di polizia/questura.
RENDEREI con:

"As what concern selling such products, you should obtain from Police Office a trade license for safety devices."

Questo è un suggerimento.
Buon lavoro, Loredana

Apart from driving licences, most other such authorisations are known as "permits". Other examples are "construction permit", "liquour permit" etc. However, note that the "holder of a trading permit, is licensed to trade in..."
Sales and distribution licences are generally granted by private companies and not the police or public authorities.
In the case of pharmaceuticals, it is known as "marketing authorisation" (M.A.)
Well, hope that was helpful.

...

:-)