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Well, the most common representation of 'point at infinity' would be a value that consists solely of zeros; that is, if normal points are encoded as a series of 64 bytes, then the point at infinity would be encoded as 64 00 bytes. On the other hand, it wouldn't appear to apply to ECDSA; ECDSA signatures consist of two integers between 1 and the curve order, ...

Standard encoding of the point at infinity is a single byte of value 0x00 (it is defined as such as least in P1363, possibly also in X9.62). Other representations may exist (such as a lot of bytes of value 0x00), but, in truth, the "point at infinity" does not have well-defined X and Y coordinates. In the case of ECDSA, you generate a random value k which ...