After reading this post, I decided to think about signalling at fast food queues. Why only fast food places? Fast food places are one of the few restaurants where there's actually more than one queue for food! At most restaurants, you're usually in one queue - perhaps in multiple queues at the same time ( one for your appetizers, one for your drinks, one for your main course, one for your dessert perhaps).
Picking up on signals at fast food places requires a little more observation than at the supermarket. At the supermarket, you can simply look at the number of items in people's baskets/carts and how many people there are in a queue - and if you go often enough, you'd probably also know which cashiers are faster, and which you can beat by self-checkout (you're usually slower, so a cashier slower than you is pretty bad).
At a fast food place, there might only be one guy in the queue - ordering for 10 people at the same table. How can you try to spot these large orders?
First things first, look at the time - if it's lunch time, dinner time, or just a time where there's a huge crowd there, there's a good chance most people, including you, are holding orders for more than one person. Try to spot groups of people - people generally talking among one another is usually telling. If you can hear what they're saying, even better. If they're talking about what to order for themselves, then it's probably not gonna be an order much larger than the group there. If they are talking about what Tom, Dick and Harry ordered, then be prepared for a little confusion and a slightly larger order.
The other thing to look for are parents - a little racial discrimination helps here - some races of people make more babies than others, so avoiding parents of a certain race will make your queue time shorter in general - most parents make relatively large orders - especially if they're without their children (i.e. their children are sitting at the table waiting with the other parent), then their orders could be significant.
You can sometimes spot groups at lunchtime by observing their name/ID tags from work - the group of 10 people wearing IBM lanyards are probably together, so are those group of 5 people wearing ING ones. This tells you a little about which queues will take longer than others - of course, they could be completely separate groups of people from the same company coming to the same place to eat - but unless the company has a particularly large presence there (you would know this if you eat there regularly) it's more probable they came together.
The other signal that's pretty useful is seeing if it's a new guy/gal at the counter - they usually have supervisors hovering around them teaching them what to do, or they might be constantly looking back to ask questions about how to do something. If you've got a large, difficult order, you should avoid them since they'll take longer to put together your order - but if you've got a simple one, go for it - people with complex orders should naturally avoid this cashier - but that's not always the case, especially during peak hours.
During most peak hours, it usually doesn't matter much which queue you're at. If you've come in a big enough group, you should queue in every possible queue, that way you'll get to place your order at the quickest possible queue. If you're alone and it's not peak hour, you're in luck, you can probably try to avoid people with large orders (there'll be fewer during off-peak) not to mention, the more relaxed pace means that there are less screw ups. :D
Not everything that affects queuing time or serving time has signals.
One thing that is difficult to watch for (if not impossible) is the complexity of the order. Some fast food outlets have a nice breakdown of what needs to be on the trays - others, do not. This could lead to plenty of problems if the cashier is not experienced, or lacks the brain power to keep track of a complex order. For example, let's take KFC's Malaysian menu. Take an order of a Snack Plate Meal, X-Meal with Zinger Burger, X-Meal with Alaskan Fish Burger, Alaskan Fish Burger Meal and a Zinger Burger Meal. Seems simple right? It's really an order for one snack plate, 2 Zinger Burgers, 2 Alaskan Fish Burgers, 2 packs of fries, 2 separate pieces of fried chicken, 2 packs of wedges and 5 separate drinks. It may seem simple now - but imagine a hectic lunch time, and while you might not miss the burgers - be forewarned - if you aren't watching, you could easily be missing fries, wedges or even the 2 pieces of chicken!
This is even without any habitual patterns forming on the part of the cashier/packer. An example is ordering apple pies at McDonalds. Most people order 1 apple pie. This causes problems when you make a complex order of several McValue Meals followed by an order for TWO apple pies. So - guess what happens if you don't check your order? That's right - you get one apple pie. It's not intentional, it's just a habit to pack one - the difference between one and two apple pies isn't that great, when you've had to pack 4 different drinks, 4 orders of fries, 1 Big Mac, 1 Quarter Pounder with Cheese, 1 McChicken and 1 pack of fried chicken.