Buttered eggs are a specialty in Cork, Ireland.
Absolutely freshly-laid eggs straight from the nest are rolled in melted butter. The melted butter forms a protective seal over the shell, extending the storage life of the eggs in the absence of refrigeration, or even if they are refrigerated. The butter also permeates through the shell and influences the flavour of the egg inside.
You won’t see clumps of butter on the egg shells; it appears as a glaze.
Buttered eggs is also the name of a dish; see buttered eggs (2).
Hens in Ireland are generally not vaccinated against salmonella, as they are in the UK under the Red Lion scheme. Instead, Ireland runs what it calls the “Egg Quality Assurance Scheme”. The scheme runs on top of already-existing regulatory requirements, and is a set of controls designed to control Salmonella spp. as well as other risk factors. The shells of such eggs are marked with the Irish Quality Assurance logo. Salmonella spp. and Eggs: Food Safety Advice for Caterers. Food Safety Authority of Ireland. May 2010, Issue 1.
That being said, there is always the risk that an egg may have come from a salmonella-infected hen, and have salmonella inside it from the start. Being stored unrefrigerated may allow any salmonella present to multiply to levels dangerous for humans. It might be best to ensure that such unrefrigerated eggs are always used for culinary purposes which involve the egg yolk and white being heated till firmly set, particularly if cooking for large groups or for “vulnerable groups, such as the frail elderly, the sick, infants, small children and pregnant women.” Ibid.