A gentleman named Johannes Haarhoff has made scanned copies of the SA Railways & Harbours Magazine from 1906 to 1967 available on this website :
https://railways.haarhoff.co.za .
This is a useful resource for anyone interested in SAR&H uniforms and badges (not to mentions trains and ships). Here are some photos showing Railways & Harbours Brigade and the SA Engineer Corps uniforms and insignia from the 1910s and '20s. (This was the original SAEC which existed from 1914 to 1916, not the present corps which was formed in 1923).
SA Engineer Corps (1914-1916)
1915 : Capt C. Burt-Andrews : British tunic with rank badges on cuffs, grenade capbadge with scroll, grenade collar dogs.
Railways & Harbours Rifles (1915-1919)
1916 : Col Sir William Hoy, general manager of the SAR&H, in full fig : Maltese cross cap badge, crossbelt plate and waistbelt plate, SA Coat of arms colalr dogas, RHR shoulder titles.
Railways & Harbours Brigade (1919-1928)
1923 : Major C.P. Heydenrych, staff major for the armoured trains : winged wheel capbadge, grenade collar dogs
1923 : Major Jack MacLean, the brigade major : winged wheel cap badge, SA coat of arms collar dogs.