Owned by millions, seen by all,
Many people are respected (I don't have actual figures but 1 in 1000 is still more than 7 million) It is easy to recognize these people.
Borne by some, and used by most.
Not everyone has (bears) respectability, but you don't have to own it to use it.
Be careful you don't blow it all, When it's your turn to make a toast.
Toasts are used to give people honor (i.e. respect), but using to much can seem insincere ("[and you] blow it all").
By day it gleams if you take heed,
If there are people around ("By day") and they pay ("take heed") proper respect, it will gleam (light is often used as an analogy of justice/righteousness).
At nighttime, cold as morning dew.
When you are alone ("At nighttime") respect is useless, "cold" if you will.
Although it may seem hard to read, Its countenance is clear to you.
It isn't always clear if you have it ("hard to read"), but you support or approve it either way ("countenance").
Salute with it, it will surpass,
Salute according to Google: "a gesture of respect or polite recognition, especially one made to or by a person when arriving or departing." When you use respect as often as you can (from arriving to departing), people will also be respectful to you. The net amount of respect will be greater than before ("it will surpass").
A bow to temper, or a kneel.
A bow or kneel are both signs of honor. When you use respect you moderate ("temper") yourself.
Now hearing many forms, at last, Its true identity reveal.
Some people are respected by some and hated (or not-so-respected) by others ("many forms"). When you hear why, the real respectability ("its true identity") will be apparent.
I'm not sure if I'm right, but I hope the effort will find some appreciation, or respect if you will ;)