Should I be concerned or on the look out for any other signs? On Tuesday 7/2/19, I found two, small to medium size, dead bees - one on my front porch and one about 20 feet away on my driveway. Unfortunately I did not take any pictures. Both areas are on either side of a flower bed which does attract a moderate number of bees and butterflies. I have not applies any pesticides for a number of years to my lawn and never in the flower bed. A few ant baits around the house and a spray ant killer on the foundation in early spring. Lawn fertilizer / weed killer was applied in early spring. Sprayed some deer repellent 3 or 4 weeks ago on 3 small trees.
We are glad that you are thinking about and noticing such things as pollinators and insects in general may be in decline.
We don't know what you actually saw, but it just may be a natural occurrence. The lifespan of some species is only a few weeks. Likewise, there are other issues such as disease which can take them.
You are wise to be careful and prudent about any pesticide use and it does not seem that you did anything that is of concern now.
Keep monitoring. We would want to hear if there was a mass die off in your yard or area.