Understanding when an abstract complex curve of given genus comes equipped with a map of fixed degree to a projective space of fixed dimension is a foundational question; and Brill-Noether theory addresses this question via linear series, which algebraically codify maps to projective targets. Classical Brill-Noether theory, which focuses on smooth curves, has been intensively explored; but much less is known for singular curves, particularly for those with non-nodal singularities. In a one-parameter family of smooth curves specializing to a singular curve C0, one expects certain aspects of the global geometry of the smooth fibers to "specialize" to the local geometry of the singularities of C0. Making this expectation quantitatively precise involves analyzing the arithmetic and combinatorics of semigroups S attached to discrete valuations defined on (the local rings of) these singularities. In this largelyexpository note we focus primarily on Brill-Noether-type results for curves with cusps, i.e., unibranch singularities; in this setting, the associated semigroups are numerical semigroups with finite complement in N.