I use to clean a church that had brick that "looked" like that in downtown Clearwater Fl for years. I used a mostly cold water at low pressure and it cleaned up pretty good. In bad areas I would spray a little Bleach 6% and water and, dwell 15 seconds or so, and then wash off. Not all brick that look alike are alike. You should be able to find out from someone that owns or manages the building what type of brick it is.
2 things I would do if I were you.
1) Do not pass go, and do exactly like Jim said reference Historical Building and contacting the local Histroical Society. Jim has given you some great advice there and it will not only help you on this job, but once completed, you'll get many referrrals from them.
2) Email the pics to Mike at Eaco Chem and get his advice before using any chem.
You could also use the BT200 on that brick with no worries of damage to the surfaces. The BT200 is certified Green and will not damage or hurt any surface and kills mold and mildew. I use it on Soft Brick applications all the time with great results. Mark at Easy Clean 916.638.0828 stocks the BT200.
No matter what you use, if this is a delicate brick, you'll want to clean in SMALL sections at a time. I personally would stay away from any type of Acid cleaner as I see grass, windows, and landscape areas, but Mike at Eaco Chem can guide you on that too.
Doug