I am absolutely sure that there are not German traffic signs (DE:437) on three roads in North Acton? The road names may be signed, but road name signs in the UK are not standard traffic signs prescribed by TSRGD (The Traffic Signs Regulations and General Directions 2016).

If no street name sign is present, you could use name:signed=no
https://wiki.openstreetmap.org/wiki/Tag:name:signed%3Dno

Tags removed in https://www.openstreetmap.org/changeset/149553238