Thanks to Nicolas Laracuente (@archaeologist) for sending me this rather atmospheric photo of some cable ties on a lamp-post in Frankfort. Once, a poster or notice was attached using them. What it was about we'll never know (a concert or theatre advertisement? Wanted poster? Changes in bus timetables?): all that remains are the cable ties.
So cable ties really are the quintessential artefact of the contemporary past: they are always used to contain or fasten or attach some kind of thing, but we frequently find them unattached themselves, having become separated from the thing as it decayed or was taken apart or moved on to other uses, other occasions. Their very presence implies the absent thing.