One way with no bells and whistles:
using Plots; gr()
p = scatter(rand(10), yerr = rand(10)/10, label="Data Points", c=:blues)
scatter!([-1],[NaN], xlims=xlims(p), ylims=(-0.5,2), label=" ")
scatter!([-1],[-1], xlims=xlims(p), shape=:cross, label="Error bars", c=:black)
