Shield cover depicted on monument??

[Matt Lukes]

Whilst recently viewing the casts of Trajan's Column at the EUR I spotted a couple of shields that appeared to have designs painted on the inner face. (Harder to see on the real monument)

The one on the far right is a wave pattern with an oval shape beneath each wave. The edge of the shield is also clearly defined. The soldier next to him also appeared to have a design too, but on closer insopection, the shield's edge was not defined

Interesting idea, but if the immediately adjacent has a different pattern on the reverse of his shield, doesn't it make rather more sense to interpret both as painted designs? The front designs of scuta on the Column are all in relief so it'd be reasonable to expect the back, if painted, to be as well.