There are four Samuel Roscoes on the 1901 England census born between 1890 and 1901 (I checked Davd and Rosco, but there were no possibles found)i:
(A) ref RG13/3601 folio 47 page 12 45 St German Street, Farnworth, Bolton, Lancashire.
Samuel Roscoe, head, 42, cotton frame minder, b Bolton - Lancs.
Mary A Roscoe, wife, 37, b Little Hulton - Lancs.
Mary L Roscoe, daur, 9, b Farnworth - Lancs.
Samuel Roscoe, son, 8, b Farnworth - Lancs.
Robt H Roscoe, son, 6, b Farnworth - Lancs.
(B) ref RG13/3755 folio 21 page 5 29 Nelson Street, St George, Manchester, Lancashire
Samuel Roscoe, head, 27, tailor's machinist, b Russian Poland.
Selina Roscoe, wife, 25, button maker, b Manchester.
Samuel Roscoe, son, 1, b Manchester.(the neighbouring household heads are Polish - looks like a community)
Two families who might be related:
ref RG17/3517 folio 123 page 21 2 court, 2 house, Moss Street, Prescot, Lancashire
James Roscoe, head, 29, gas works stoker, b Prescot.
Roseina Roscoe, wife, 27, b Covenrty - Warwickshire.
John J Roscoe, son, 6, b Prescot.
Walter Roscoe, son, 4, b Prescot.
James Roscoe, son, 2, b Prescot.
George Roscoe, son, 1, b Prescot.
(C) ref RG17/3517 folio 123 page 21 3 court, 2 house, Moss Street, Prescot, Lancashire
William Roscoe, head, 34, watch tool maker, b Prescot.
Elizabeth Roscoe, wife, 29, b Whiston - Lancashire.
James J Roscoe, son, 9, b Prescot.
Thomas Roscoe, son, 7, b Prescot.
Samuel Roscoe, son, 5, b Prescot.
Lilian A J Roscoe, daur, 2, b Prescot.
William B R Roscoe, son, 6mo, b Prescot.
(D) ref RG13/3809 folio 7 page 6 26 Essex Street, Oldham, Lancashire
(head of household not listed)
Mary Roscoe, wife, 27, b Oldham.
Wilfred Roscoe, son, 5, b Oldham.
Samuel Roscoe, son, 1, b Oldham.
On FreeBMD there are six Samuel Roscoes born between 1890 and 1901:
1) Samuel Roscoe, Mar 1893, Bolton, vol 8c page 375 (probably matches Samuel in (A) above)
2) Samuel Roscoe, Mar 1896, Prescot, vol 8b page 701 (probably matches Samuel in (C) above)
3) Samuel Roscoe, Jun 1898, Wigan (Lancashire) vol 8c page 65 (died aged 2, Wigan, vol 8c page 27)
4) Samuel Roscoe, Dec 1899, Oldham, vol 8d page 658 (probably matches Samuel in (D) above)
5) Samuel Roscoe, Mar 1900, Manchester, vol 8d page 297 (probably matches Samuel in (B) above)
6) Samuel Millward Roscoe, Sep 1901, Bolton, vol 8c page 373 (born after the census was taken)
Allowing a margin on the ages, this leaves you with five possible Samuel Roscoes to choose from. Unless the US military records can narrow the search down, the only other way I can think of to help decide which one is yours would be to order the birth certificates and hope that his middle name or his mother's middle name is given.
All the best
Philip