LK1,LK2,LK3 are optional links on the CPC mainboard, connected to PPI Port B, Bit1-3. The links select the distributor name (which is displayed by the BIOS in the boot message).
These LKs exist on all CPC mainboards. By default, LK1-LK3 are not installed (Amstrad). Other combinations are LK2 installed in german Schneider models, and LK1+LK2 in australian Awa models.
Please take a look at www.retrocomputers.eu for more info about my retro computer collection.