What's a proper etiquette when approaching a manufacturer at a show? Well, I have done some research and found some good tips and tricks from art licensing professionals. It's also common sense in any business.
RIGHT WAY: Approach a manufacturer at a booth when not already engaged in a conversation; ask: "Can you give me the name and contact info of the person responsible for reviewing new art as I'd like to contact them after the show." (or something along that line)
WRONG WAY: Don't walk up to people in the booth if they are already busy in a conversation with other people and ask for info or to review your portfolio. Aside from being rude, it's also a sure way to create a bad impression with both manufacturer and guest being entertained ... you never know who that might be.
OCCASIONAL WAY: You might be asked to go see someone else who is nearby when asking the contact. If that happens, kindly thank them and go introduce yourself. Ask for that person for their contact info, again stressing that it's for after the show. Sometimes they will look at your work then and there, but normally they will give you a card to use for contacting them at a later time.
ADDITIONAL WAY: Do your homework before walking the show. Find out about a company's products and customers ahead of time. You should know and understand what they do; you want to show them quickly that you get their products/materials and that you can show them rapidly how your art might fit in to their company's products or market demand.
Also, have a good sample visual/small package of your work along with your card, something that will catch their attention. It should be a good representation of your work and that should be something they can store away easily yet allows them to remember you at a glance as they go back to their office. Otherwise it could take up weeks to look you up again.
At last, make sure you bring your portfolio nicely presented or in digital format (tablet) to the show in case you get "lucky" and get to present your art on the spot!
As they say, "Chance favors the prepared mind."