The same picture appears in 'The Tramways of Birkenhead and Wallasey' by Maund & Jenkins.
The caption for it reads -
"Experimental windscreens were fitted to two [tram]cars late in 1913. The one used on No. 28 was similar to those used in Aberdeen (note the hand holding the screen in position.) The second was designed and made at Laird
St. depot and fitted to No. 25. (Courtesy E. Gray)
To be honest, I read it in the text first, then looked more closely at the picture.