Seattle has a long tradition of informal, "outsider" art, of which show flyers are probably the most transitory, yet most visible.  Artists such as Art Chantry and Jeff Kleinsmith established definite aesthetics (and even movements) through the advertising for rock shows (thankfully displacing the psychedelic f---in Grateful Dead show flyer as the dominant paradigm).  Heck, I still have flyers they (and others) did at my parents house, documenting the great scene years ago, even if I wasn't old enough to go to most of the shows. 

In flyering for our upcoming show (plug: 11/11/06, the Comet Tavern), I was yet again frustrated by the complete lack of respect practiced in flyering.  Remember, flyering was made illegal only a few short years ago, and one of the main arguments to overturn that was based around ideas of community expression and access to public space, not to allow you to plaster a million copies of the same damn flyer on one telephone pole. 

So, I've tried to codify some of what I see as an etiquette of flyering, which should all be common sense and fairly obvious.  (Like asking people in businesses if you may put up a flyer at their store and thanking them when they do so).  Here goes:

As a general rule: don't flyer over other flyers.

Exceptions to this rule:  If…

1. There are more than two flyers for said event on the same telephone pole. (Comment: Plastering the entire street and all space makes you a ball hog and you are greedy, greedy!)
2. The show is more than a month away.  (Comment: Patience… monopolizing space for more than a few weeks doesn't help much.  Unless there are advance tickets and it will sell out, in that case, you don't really need to advertise, do you?)
3. The show is at a huge venue/EnormoDome (in Seattle: this would include the Moore, the Showbox, KeyArena, the Pier, Whatever Amphitheater).  (Comment: These places obviously have advertising budgets and foot traffic isn't going to make or break the success of the show.  Or rephrased: the price of one ticket with surcharge is higher than what we'll earn for our little club show, so there).
4. The band is a huge major-label act.  Or has appeared on Letterman.  Or is on the Warped Tour.  (Comment: See previous two comments).
5. The event (or band) is sponsored by a corporation, prominently displayed on the flyer.  (Having Alaska Airlines associated with a singer-songwriter has no place on a telephone pole.  Sorry.  Maybe put flyers in the napkin/silverware packet.  Come to think of it, wouldn't it make more sense for an airline to advertise shows that are out of town?)
6. The show has already sold out.  (Comment: Flyering over it is actually a service to the people who don't have tickets.  You spaced buying a ticket, now time to excise it from the public consciousness, because I spaced it, too).
7. The show happens within the next 9 hours.  (Comment: People already know about it or don't, if your friends somehow "forgot" they are sure good "friends.").
8. The flyer is super glossy and looks like it cost a ton to print.  (Comment: what is it doing on a telephone pole?  Flyering is the advertising of the poor, huddled masses with a certain (misplaced) nostalgia for punk DIY-ness, not Mr. "I might as well just staple dollar bills to the telephone pole").
9. The event is a repeating, non-live music event, i.e., wacky '80s nite with DJ Take My Breath Away.  (Comment: this is a grey area, to a degree.  Don't methodically cover them all up, but don't feel bad about covering up a couple.  If they're glossy and fancy, go right ahead.  Pioneer Square doesn't need your help). 
10. This same flyer has been put over other, valid show advertising, or has otherwise broken the code of conscientious flyering.  (Comment: none needed).