Indeed it does.....stands for (River) Tweed.
Another river-based postcode is TS - Tees or Teesside.
Some other area-based postcodes:
DG - Dumfries & Galloway
HS - (Outer) Hebrides
FY - Fylde
ME - Medway (as opposed to Maidstone - ME1 is Rochester)
SP - Salisbury Plain
ZE - Zetland (archaic spelling of Shetland)
KW is an oddity; although the postcode area is named Kirkwall after the town on the Orkney Islands, the Post Town is actually Wick, on the mainland, which has the postcode KW1 - indeed most of the KW postcodes cover Caithness and Sutherland with only KW15-17 allocated to the Orkney Islands. Some people assume that the KW postcode for Wick must be a mistake and invent WK postcodes, which of course don't exist!
CR0 was originally designated CRO (i.e. letter O instead of number 0) as it was issued experimentally in the 1960s. It was recoded in 1974.
Glasgow was given compass-point postcodes similar to London in 1923: C, W, NW, N, E, S, SW, SE. These were changed in the 1970s, with C1-C5 becoming G1-G5, W1-W5 becoming G11-G15, NW becoming G20, N1-N3 becoming G21-G23, E1-E4 becoming G31-G34, SE becoming G40, S1-S6 becoming G41-G46, SW1-SW3 becoming G51-G53.