A pair of well-worn working boots
I've often had a metaphorical cuff round the ear from my wife for doing exactly this, but until recently I had no idea why I must suffer so.
It has been suggested by a reader that the tradition/belief originates in the habits of mining and manual labouring communities - which may explain its lingering presence in the North in particular.
"When I was a small child my father worked for the British Coal Board as an engineer, and I was frequently chastised if I ever put my shoes on the table, when I asked about it my father told me that in mining communities the only time boots or shoes were placed on the table was when the family was informed of the death of a miner. His boots would be placed on the table to show he was dead. After that placing shoes or boots on the table was seen as either tempting fate or in poor taste. Seeing someone's shoes on the table could severely frighten someone if they didn't know that the person was alive and well."
Digging a little deeper, it seems that working men in earlier times would generally possess only a single pair of work boots. In an era prior to mass-production, they would have been quite individual in appearance.
Thus - it is suggested - they would be a means by which a person could be identified without necessitating the need for someone to identify an actual body.