Just found a new cache of Siddhaṃ calligraphy on YouTube (thanks to Riccardo's Facebook page Bonji 梵字 - Riccardo is a bit naughty and has been taking images from here without asking, but I'm sure we can sort something out). These are quite interesting examples which from the accompanying text and commentary are from Japan.
The Fudō Bīja hāmmāṃ
The Mahāvairocana Seed Syllable vāṃḥ
Note here that the calligrapher makes an error. He writes ba instead of va. The two are very similar. In ba the curve curls back to meet the stem on the up-stroke, whereas on the va it continues down to the stem on the down-stroke. These letters are similar in most Indic scripts: cf Devanāgarī ब व. Indeed they are often confused in pronunciation as well.