Nark,
You wrote: The "sign of the Son of Man" in Matthew 24:30 (distinct from the astral events in v. 29) is generally understood as the very coming of the Son of Man (compare the parallel in Mark 13:26, "Then they will see 'the Son of Man coming in clouds' with great power and glory") ...
Understanding scripture is, of course, tricky business. When Christ said "Then they will see the Son of Man coming" he did not necessarily mean, "Then they will see that he has come."
My car has been making a lot of noises lately. So I see some repair bills coming. In saying that I do not mean these bills have already arrived. I mean I am sure they will arrive soon.
After discussing the astral events and specifically referring to "the sign of the Son of Man" in verses 29 and 30, in verses 32 and 33 Jesus said, "Now learn this lesson from the fig tree: As soon as its twigs get tender and its leaves come out, you know that summer is near. Even so, when you see all these things, you know that he is near, right at the door."
Remember, Christ's apostles had asked him, "What will be the sign [singular] of your coming...?" They were obviously looking for some sort of forewarning. (Matt. 24:3) Christ then told them that "the sign of the Son of Man will appear in the sky." The sight of Christ himself appearing in the sky would not be a 'sign of his coming,' it would be his coming.
You wrote: not the umpteenth "sign" that he is coming "soon".
Jesus did not give multiple "signs" of his coming. Neither did he give a "composite sign" as JWs and others tell us that he did. Christ's apostles asked him for a singular sign and that is what he gave them, a sign that he said would "appear in the sky."
Matthew 24:4-8 in The Message Bible renders his words this way; Jesus said, "Watch out for doomsday deceivers. Many leaders are going to show up with forged identities, claiming, 'I am Christ, the Messiah.' They will deceive a lot of people. When reports come in of wars and rumored wars, keep your head and don't panic. This is routine history; this is no sign of the end."