All Glyphs needs to be shared between all character on the same account, but not beween softcore and hardcore, and not between Eternal and Season. If you play many characters and level them up differently it is just to boring to level up glyphs in only one way, and have to start over leveling glyphs on every character. Glyphs leveling should at least be done passive, like the barb leveling different weapons by just doing any content in the game.
A Glyphs level progress on Season character are added to Glyph level progress on Eternal, after the Season ends.
A Blue (magic, not rare) glyph needs to be tradable.