Bright light extending from dark cloud formation over river, moving very slowly and deliberately

Saw bright light, in blade-like form, extend from dark cloud formation hanging over Hudson River (near NYC's Columbia Presbyterian Hospital). The blade of light moved very slowly and deliberately to cut what appeared to be a rectangle out of the cloud, leaving a bright outline. Then a symbol was created by the blade, made of very bright, light clouds, within the rectangle. It appeared to be a symbol, sort of like the Han alphabet (but not that). The blade moved behind the dark clouds and slowly faded. The cloud symbol faded a minute or two later. Observer--female, age 64.