This is posted in the waiting room of an Irish hospital. Interesting glimpse into their culture.
The full text of the poster
This symbol has been developed by the Hospice Friendly Hospitals Programme to respectfully identify the End of Life.
This symbol is inspired by ancient Irish history; it is not associated with any one religion or denomination.
The white spiral represents the interconnected cycle of life, birth, life and death.
The white outer circle represents continuity, infinity and completion.
Purple has been chosen as the background colour as it is associated with nobility, solemnity and spirituality.
In this hospital the symbol may be displayed on a ward to add respect and solemnity during end of life or following the death of one of our patients.
It's called reconstructionism, and it's not uncommon in neopagan communities. Most of them are pretty honest with themselves about the limitations of their knowledge. It's not fraudulent at all.
Anyway, Roman accounts are one source we have for studying celtic culture, but it's not the only one. There's also archaeology. There's some of the mythology that survived. There are old Celtic stories that got christianized by the clerics who recorded them for the first time. There are surviving superstitions and folklore that some ethnologists recorded in the 19th and 20th centuries.
Each of those things provides insights into the beliefs and practices of the pre-christian Celtic civilizations. None of them are a full or a complete picture, nor even all of them together. But if each one together clarifies the picture a little more.
There's always a limit to how much we can know about prehistoric cultures (in the sense that they had no writing system until converting to christianity). But that doesn't mean it's pointless to study them.