Welsh republican activists have defaced road signs to "eradicate imposed" English language place names.
It claimed responsibility for its actions on their Twitter page.
The group told ITV News that after the "official restoration of Bannau Brycheicinog's name (and the ensuing anger that followed), the group "believed it was necessary to highlight that there are many places in Wales that still bear English names".
"Most of these names simply describe the same geographic feature as the Welsh name, others are offensive transliterations of the Welsh and some are wholly artificial names conceived in Victorian times."
The group launched last December, saying: "Announcing the launch of Yr Eryr Wen, a Welsh youth organisation campaigning for the creation of an independent Welsh republic and for the protection of our language, culture and identity.
"We are committed to achieving our aims through the use of provocative and non-violent activism and are open to applications to get involved..."
The group told ITV News that by covering the signs, it has "both started a debate and also protested against those who were angered and offended by the restoration of Bannau Brycheiniog".
"It was similar protests such as these that resulted in the removal of the archaic use of the name 'Carnarvon' in the seventies.
Yr Eryr Wen is Welsh for the "White Eagle" - an emblem most notably associated with the Welsh nationalist organisation the Free Wales Army. Historically the emblem represented the eagle of Eryri (Snowdonia) which in Welsh mythology is said to protect Wales.
Group members were present at a second homes and anti-coronation rally in Caernarfon last weekend where they said they stood "alongside Cymdeithas yr Iaith in declaring that Wales is not for sale".
When asked if the group is worried about possible criminal proceedings, a spokesperson said "it's a risk that we've willingly taken".
"As recent events during the Coronation have demonstrated, the state is becoming increasingly willing to crack down on our right to protest, so we believe it imperative to take a stand, regardless of what the authorities may do. Given the attention that this simple protest has already generated, it clearly works in bringing attention to the issue as intended."
A spokesperson for Gwynedd Council confirmed work to repair or clean any damage will be carried out as soon as possible.
“The Council’s language policy was reviewed in 2022, reaffirming our commitment to protecting Welsh place names. As part of this, the Council will be taking into consideration appropriate changes to road signs as they are renewed or repaired, so as to use Welsh place names only.
“Cyngor Gwynedd’s Place Names Project is responsible for a range of matters in relation to protecting original and indigenous Welsh place names – from trying to ensure that house names are not changed from Welsh, to raising awareness of the varied and fascinating names that local people have for places and features which do not appear on standardised maps.