This object was found on the site of the "high place" (sanctuary) at Gezer, west of Jerusalem. It is a sherd, from a cylindrical cult stand, dated to the Middle Bronze Age (before 1600 BCE).
There are three characters of the proto-alphabet inscribed on it. The one at the top is a hand showing its palm (kap) and thus K. The bottom letter is a square, representing the ground-plan of a house (bayt) and hence B. The middle sign might be W (waw, a hook), or L (a crook or a coil of rope); but the head is rather small for either of these choices (W or L); it is better to see it as a snake (nahhash) and so N.
While the inscription is commonly read as KLB, offering Caleb as the name of the donor or maker of the cultic object, the reading BNK would produce 'thy son', as a reference to the person donating the stand to the temple.
Nevertheless, my proposal is to understand the text in this way:
KN B "Temple stand"
Remember, this was a cult stand found in a sacred place, and KN corresponds to the Hebrew word ken "stand" (Exodus 30:18, a bronze stand for a basin, in the sanctuary).
The house-sign is an example of a logogram, standing not for the first consonant of the word it depicts (B) but for the whole word, bayt, meaning "house" or 'temple". So the word 'house" qualifies "stand" as a "temple stand".
Another possible example of proto-alphabetic B as a logogram occurs on a small female sphinx from the temple of the Sinai turquoise mines (inscription 347a; Colless 1990, No 6 ).
The L (preposition "to" or "for") is above the B (square house, a logogram for bayt).
L B(ayt) "For the temple"
The word bayt was also written in full (without the vowel a, of course). One example is on a sherd found in the ruins of a palace at Lachish (Colless 1991, No 10).
This seems to say the same thing (reading from right to left):
[L] BYT "For the house"
As the sherd was found in a palace, that might be what "house" refers to in this case.
The word bayt (or bayitu) was also written without the Y, as on the Beth Shemesh ostracon, where we have BT YN (properly byt yyn) "wine house". Perhaps the medial y was considered to be a vowel (it is actually a "semi-vowel") and therefore omitted, as the proto-alphabet was a consonantal script.
Brian E. Colless, The proto-alphabetic inscriptions of Sinai, Abr-Nahrain 28 (1990) 1-52. (Available as pdf from Peeters)
B. E. Colless, The proto-alphabetic inscriptions of Canaan, Abr-Nahrain 29 (1991) 18-66. (Available as pdf from Peeters)