A SIGN OF THE TIMES is the one-way caller.

Person leans into the three-sided coop we used to call a telephone booth, squints to see what kind of machine it is, punches rather than dials a number, then waits. He or she fumbles for a pen and something to write on as a couple of rings go by. In a moment, the caller straightens to attention and receives instructions. Then the caller's fingers punch a few buttons; another brief wait; more punching, then a long listen, a smile or frown, and another punch. Not a word is spoken into the receiver.

The caller is either a K.G.B. agent under intense surveillance or your average user of a telephone message service. I have one, called Audix, or Unix, or Felix -- there's an x at the end -- and I no longer need other people. I just leave and get messages; I could be gone for years, and nobody would know.

The caller presses the numeric keys with his secret password, which is often the day and month of his birth, the easiest code imaginable to break, but it transmits a sense of confidentiality or satisfies some other mes sage-service need. (Go memorize an irrelevant number; if you forget and have no mnemonic, you will be frantically banging on the numeric keys; it's a piteous sight.)

"Please enter your password," the synthetic-syrupy recorded voice directs, "followed by the pound sign."

"When was I born?" is my first internal question. The second, which I asked only once, was: "What and where is the pound sign ?"

I always thought the pound sign was the symbol for the British pound sterling, a script capital L with a hyphen through it, a stylized representation of the Latin libra . (The Roman pound was several ounces lighter than the modern pound; some things stick in my mind, but numbers fade fast.)

No; the sign that the recorded Miss Syrup refers to is what some of us remember as the tick-tack-toe sign , or the crosshatch , or the sign of the double-cross , similar to the symbol Charlie Chaplin wore as a parody of the swastika in his 1940 movie, "The Great Dictator." Willard Espy, the Valentino of word lovers, has built on this thought in Harvard Magazine to suggest proditio , Latin for "betrayal," or double-cross. Nice try; won't fly.

When #, as we shall call it here, is placed before a number, it is called a number sign ; #1 pencils have a softer lead than #2 pencils, and nothing fits into a #10 envelope anymore. When a musician sees it, the meaning is "sharp"; doctors often use it as a symbol for "fracture."

When a proofreader uses the #, the meaning is "insert space here": two words incorrectly runtogether are happily separated by a #. (When this copy comes to the proofreader, whose legendary name is Mr. Dunphy, that eagle-eyed worthy will circle runtogether , run a line out to the edge of the page, and put a # at the end. Another editor, with a profound sense of context, will write "stet" over that, meaning "leave as is," from the third-person present subjunctive singular of the Latin stare , "to stand." I get a lot of sweaters for birthday presents; think I was born in December.)

In internal memoranda, the telephone company (a locution left over from the days of A.T.&T. monopoly; there are now hundreds of telephone companies) likes to use octothorpe , also spelled octothorp . Octo- is a combining form for "eight," as octogenarian octopuses know, and refers to the eight points around the outside of the symbol. But there are nine spaces in a tick-tack-toe game. The crosshatch has 12 line segments. Forget octothorpe .

Pound sign , however, is catching on. The origin may be from the use of # to mean "pound," as in "a 5# bag of sugar," written by someone unhappy with the abbreviation lb. to stand for "pound." (We know that pound is from the Latin libra pondo , "a pound by weight," which accounts for the lb. ; not everybody knows that. The week before Christmas is when I was born.) This would not be the first time the weight of a pound was used to form a noun phrase; in pound cake , the original 1747 recipe called for a pound of butter.

A more remote possibility is that pound evokes a mashing of the desired button, as one pounds on a door, but I go for the 5#-bag theory.