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I find the observation that no globulars could be seen in a Hubble Telescope image of M104 rather puzzling.
Bear in mind that even the (small number of) very largest globulars of M104 are only 1 arcsecond across, and many of the globulars are much smaller than this in angular size......in other words, these clusters will look exactly like stars in the telescope and in images of M104.
The only thing that allows us to distinguish this galaxy's system of multiple globular clusters from the foreground stars is the unusual distribution of very faint point sources surrounding the Sombrero. Of course, if you happen to have access to the HST with its 0.05 to 0.1 arcsec angular resolution, you can actually see some of these globulars as extended sources!
It is unfortunate that NGC5128, which is at 40 percent of the distance of M104, has so many faint foreground stars around it, as this makes its very rich population of globular star clusters impossible to see due to confusion with foreground stars. (N5128 has more than 1500 globulars, though the exact number is not yet certain)
Incidentally, if you go to //arxiv.org and look up the preprint with the Identifier arxiv 0901.1693, you will find that an unusually extended "globular cluster -like" object belongs to the Sombrero. This is an Ultra Compact Dwarf (UCD) galaxy, and these objects are half way between a globular cluster and a faint elliptical galaxy, in their properties. An UCD galaxy is usually several times the diameter of a very large globular cluster.
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