The TrigpointingUK database contains a few artefacts which are not actual survey marks, but which are interesting nonetheless. Robs Pillar is one such item. Another is a wooden pillar (with genuine Spider and FB) at the National Library of Scotland, whilst a pillar with genuine FB can be found at Newcastle University.
There are also some genuine OS trigpoints that do not fit into any of the standard categories and are termed 'Other'. In TP:UK this is a generic category that encompasses a number of specific types; 55 items are listed. 'Other' is not a type of mark in OSGB36; the corresponding types include Holes, Marks, Pegs, Posts, Punch marks and Topographs.
There are also number of oddities, for example:
Bovingdon Green a passive station which might have been a threaded rod; Stornoway Bench Mark described by visitors as a dustbin lid or drain cover; Hemmingfield recorded in OSGB36 but a mark was not installed; Gob a Gheodha which could be a phantom trig; Glyder Fach recorded in OSGB36 as a bolt but appears to be a brass ferrule.