Since the adoption by Ireland of metric speed limits, warning signs have been placed on either side of the border to alert motorists to the change to or from miles or kilometres per hour. As the United Kingdom does not use the euro, advertised prices for service stations and shops will change currency on crossing, although many places along the border will accept cross-border currency informally (albeit usually at a rate favourable to the trader). Other typical signs of crossing a European border are also noticeable. These include subtle differences in the paving materials of road surfaces and pavements, sometimes with visible differences in colour between materials across the border, changes to street lighting when crossing the border, (though these also vary across inter-county borders), and changes in the colour of postboxes (green in Ireland, red in Northern Ireland).