"Many, many times my agents have worked on a case and didn't know who else was working with them," the Colonel began presently. "And often they got in tight corners and needed help badly. So--But hold it a minute. Let me mention something else right here. When I say tight corner, I don't mean that the agent is about to be caught, or about to be killed. I mean _more than that_! I mean when he gets in a spot where _valuable_ information he has collected may be lost unless he gets help. Or when something is about to happen that will seriously harm his country unless he gets help. That sort of thing. _Not_ the present or future welfare of the individual agent. You see what I mean?" "Yes, sir," Dave replied, as his stomach suddenly felt a little hollow and empty, and his mouth went just a little bit dry. "Help to save your country, but not to save your own life, eh?" "Exactly," the senior officer said, and nodded at the two orange-headed pins. "That pin is an agent's SOS sign when _all else has failed_. Keep that hidden on your person at all times. If the occasion ever does arise when you need help in the way I described, take that pin out and stick it in the right side of your shirt collar. If you're not wearing a shirt, then in the right side of the top of whatever garment you're wearing. In short, so that the orange head of this pin is nearest the right side of your face. If there is another agent near by, he will immediately make himself known by placing his pin in the exact place where you have put yours. "Remember that. Don't forget it for an instant! If you need help, place this pin at the top of whatever garment you're wearing where it will be nearest the right side of your face. Even if you've only got a pair of pants on, put the pin in the right side of the pants at the very top. That clear?" The two youths nodded. Then Freddy Farmer leaned forward a bit, and stared questioningly at the Colonel. "Supposing, sir, you see the SOS pin on another chap," he said. "In the right place, of course. But supposing it may interrupt your own work to make yourself known to him. What then?" "Establish your identity, regardless," Colonel Welsh replied bluntly. "That is a fixed rule in this department. And here is why. Because of what the SOS pin stands for: a last appeal for help when the welfare of the U. S. is in serious peril. I know what you're thinking. Your own case may be just as important as the agent's who is appealing for help. That is the chance we have to take, though. That is why the SOS pin can only be shown as a desperate last resort to forestall a great military and naval calamity. And to give you an idea of what I mean, I know of only two cases when the SOS pin was shown during the fifteen years I have been in this department. True, the coming of war will increase the possibility of the SOS pin being shown. But--well, that's for the future to bring to light. Now, let's have another question."