"Loco" means "in the written octave", as opposed to shifted by some number of octaves. Such a shift could be due to 8va/8vb marks, or in this case, because of instrument transpositions. Tenor sax sounds an octave lower than trumpet, so by writing both instruments on a single staff there's an ambiguity--are those tenor sax notes in the trumpet octave or the tenor sax octave? This mark means "in the written octave", so in the trumpet octave. The proper tenor sax part will be written an octave higher.
The second example is unclear, since Eb clarinet and sopranino sax transpose exactly the same. I guess this means that the clarinet is on the upper line and the sax on the lower, but that would be a clunky way to write that.