Interesting news that that
sign is to make a comeback in Ireland to mark the default 80 km/h rural speed limit. There had been many complaints that 80 km/h signs at the entrance to tiny rural lanes looked ridiculous and were likely to bring the whole system into disrepute.
http://www.rte.ie/news/2013/1121/488146-speed-limits/Edit: from the official statement, it looks as though the national guidelines will be made mandatory on local highway authorities, and there will be an appeals procedure against inconsistent limits, both of which we lack in the UK:
http://www.dttas.ie/press-releases/2013/speed-limits-review-body-publishes-report-recommends-new-appeals-system