[H2O]

It's possible they are there to aid the architects in selecting the glass they are specifying. Usually glass is chosen with small samples inside an office, but the appearance of glass can differ greatly in natural light, and large panels may differ in appearance from small samples due to the influence of the edge materials on the small samples.

I take it as a sign they are progressing on the design process, and taking the appearance of glass seriously enough to bother having glass shipped to the site for inspection.