Keeping numeric type when adding a character symbols in R

This is an example:

df <- structure(list(Longitud = c(-179.75, -179.75, -179.75, -179.75, 
-179.75, -179.75), Latitud = c(71.25, 68.75, 68.25, 67.75, 67.25, 
66.75), Enero = c(-23, -26, -25.9, -24.1, -24.8, -21), Febrero = c(-25.7, 
-28.7, -27.6, -25, -24.8, -20.1), Marzo = c(-24.3, -26.7, -25.9, 
-23.5, -24, -20.3), Abril = c(-17.9, -20, -19.3, -17.1, -17.4, 
-13), Mayo = c(-7.1, -7.8, -8.6, -7.7, -9.1, -5.8), Junio = c(-0.1, 
0.1, 0, 1.2, -0.4, 2.6), Julio = c(1.8, 3, 2.9, 4.5, 3.4, 6.7
), Agosto = c(1.4, 1.7, 2, 3.8, 3, 6.8), Septimbre = c(-1.7, 
-1.9, -1.8, -0.2, -1.6, 1.4), Octubre = c(-8.2, -10.4, -9.7, 
-7.6, -8.4, -5), Noviembre = c(-15.6, -18.2, -17.5, -15.3, -16, 
-12.4), Diciembre = c(-22.2, -25.5, -24.5, -22.2, -22.4, -18.2
)), .Names = c("Longitud", "Latitud", "Enero", "Febrero", "Marzo", 
"Abril", "Mayo", "Junio", "Julio", "Agosto", "Septimbre", "Octubre", 
"Noviembre", "Diciembre"), row.names = c(NA, 6L), class = "data.frame")

Columns from Enero to Diciembre are numeric. I would like to add in all those values in those columns the symbol Celsius in the end (º). But I would like to add it without converting the column to character, so that I can keep working with the numbers.

Is there any way to print this symbol and to keep the numeric type?