Each hero has five glyphs. They boost main and secondary stats. To unlock glyphs, you need to upgrade the hero's rank.
The maximum glyph level is 50.
To level up a glyph, you need emeralds or runes and gold. From the beginning, you can upgrade a glyph only to the 30th level. When a hero reaches level 60, you can boost the glyph up to level 40. Glyph levels 41-50 become available when your hero gets to level 100.