Speech research has shown that vowels are less categorical than consonants, but a similar correlation in sign, i.e. between handshapes and place of articulation, is not yet known. The handshapes seem similar to vowels: they are continuum-like and follow coarticulatory principles. Here categorization and discrimination of handshapes were studied from the perspective of vowel perception. According to the results handshapes from the Finnish Sign Language handshape continuum transcribed as /G/-/X/ are perceived similarly than vowels varying systematically along a phonetic continuum. As in vowels, a phoneme boundary between signs can be found. In addition, there is a tendency for enhanced discrimination at the boundary zone. However, these results are typical to native signers only.