In the past runes had a charge and each rune has its own number of charges and if a rune had more than this preset number of charges it became a “overcharged rune”
Some of this overcharged runes could be obtained in PoI and others were loot of Ferumbras when it was controlled by someone from Cipsoft (when it wasn’t a creature)
The overcharged runes had the same purpose as regular runes they only had more changes than the ones created by mages or bought at stores
When the runes and potions became stackable they decided to change all overcharged runes into silver/golden runes emblems and some are still obtainable in game(only in quests like POI) but most are only obtainable in fansites contest/events