I have found printable cards for communicating dietary restrictions in Japan.

I would like to know how exactly a card like this could be used in a restaurant, keeping in mind that in Japan politeness is very important.
As soon as I enter the restaurant? Wait until the waiter takes my order?

Any advice is appreciated.

I have found printable cards for communicating dietary restrictions in Japan. How exactly could a card like this be used in a restaurant, keeping in mind that in Japan politeness is very important?
As soon as I enter the restaurant? Wait until the waiter takes my order?