Salts Mill used to be a thriving textile mill, from 1853 when it opened right through to 1986 when closed down. During that time it had various owners and the company had various names but the Belwarp logo, with its lion and bell, was used for much of the time. It is immortalised in the fabric of the building, carved in stone on the south face, above what is now the All Terrain Cycles shop.
Belwarp Serges were advertised as being "guaranteed in fast colour and unshrinkable to a greater degree than any other serges on the market. In England and on the Continent these serges are preferred before all others. No lady's wardrobe is complete without a 'Belwarp' serge dress." Serge is a high-quality woollen twill cloth. The heaviest versions were used for military uniforms. There is a poster advertised for sale on Amazon, from a newspaper of 1890, which shows the Belwarp lion advertising Belwarp serge made by John Maddocks & Co. John Maddocks was one of the businessmen who took over Sir Titus Salt, Baronet, Sons & Company Ltd when it went into receivership in 1892, so it's possible that the lion logo came along at that time. I don't know for sure. I've also found a snippet in the Sydney Morning Herald 1903 which speaks of a Sydney tailor, Mr D T Grant, using Belwarp serges so it sounds like they were exported right across the world.
I took the photo of the poster above at a Christmas event in the Victoria Hall (which explains the bells!). It is part of the Saltaire Archive held by Shipley College and I believe this advert dates from the 1950s.