how does DSD silence looks like?
DSD bits are 0 and 1 indeed, but they actually represent normalized outputs of -1 and 1, respectively, since one-bit samples can only be mid-raiser-quantized. This means DSD samples cannot represent zero. One can generate DSD silence by alternating 0-s and 1-s (your second option), or by a 1-bit delta-sigma modulation of a zero PCM input, with or without dithering (your third option).
Multi-bit modulators can (and normally use) mid-tread quantization, so they can represent zero. Thus, multibit silence is either a sequence of zeroes or the output of a multi-bit delta-sigma modulator presented with a zero input.