This bowl is acidmarked "BM Plus Norway" which is the series produced at Plus in Fredrikstad from Motzfeldt's "unike" prototypes. She stayed at the glasshut for a coulple of days designing new glass and these were marked with a quite simple engraving "BM XX", XX beeing a two digit year. Then the glassblowers made these in series until her next stay. These series are acid stamped "BM Plus Norway".
BM XX signed items can reach prices as high as £500-1000 in Norway, although most of them sell at about £150-£250. Acid stamped BM-plus items are cheaper, £20-£150 depending on size, colour and general interest from collectors.
Some small series and unike Randsfjord items are marked "BM XX", but most of her Randsfjord production is sticker-marked. Randsfjord items have a round polished puntil mark while plus items are quite rough.