There are plenty of these forms in WO 363 (First World War service records), WO 364 (pension records) and, of course, WO 96 (militia attestations). The militia, replaced by the Special Reserve in 1908, was an ideal testing ground for many men who wanted to see if they were suited for army life, but without the full-time commitment.
The forms are very similar to the forms used by the regular army, and give that essential detail so beloved by family and military historians: place of birth, place of residence, age, occupation... in short, all the essential detail that can act as a springboard for further research.
The papers in WO 96 are certainly the best preserved and I think in general that this series can often be overlooked. To my mind, it's always worthy of further investigation and on more than one occasion I have discovered papers here for a man whose First World War papers went up in smoke in 1940.
In common with other army forms - and attestation forms in particular, Army Form E.504 went through various iterations and amendments. The version I have reproduced here dates to April 1891 and was the 13th variant of this particular document.
Images reproduced on this post are Crown Copyright, The National Archives.