WW2 German Military Symbols can be very confusing, with certain symbols only being used for specific types of maps, and many symbols also being superseded over time. The symbols on your map range from symbols for vague, unknown or general defensive position indicators, to some very specific position types. The Military Intelligence Research Section published a pamphlet in 1944 called "Supplements: German Military Symbols". The Germans had hundreds of symbols for their own units, and according to this pamphlet had specific symbols for certain types of enemy positions for which intelligence may not be complete. On page 223 under "Map and Aerial-Photo-Overlay Symbols Indicating Enemy Fortifications, etc." it shows examples of the symbols found on your disposition map. One of the most common markings is the small red triangle which means "Klein-Kampflanlage" which means "Supporting Defensive Installation".

The Military Intelligence Service pamphlet "German Military Symbols 1943" is a bit more clear about some of the specific symbols. On the lower right hand corner of your map, in the area marked 'Pobyli' on the eastern side of the Volga, there are some emplacements along the river bank. On page 16, these symbols appear as "Heavy Machine Guns in Position" meaning an MG in an entrenched or prepared position. Page 130 of the the Military Intelligence Division pamphlet "Company Officer's Handbook Of The German Army" shows some very clear descriptions of some of the superseded symbols we see on the map. The symbols seen around the location 'Poblyi' on your map appear to be 37mm Anti-Aircraft guns in fixed positions. There is also a Heavy Mortar position marked with a question mark as a 'doubtful' or 'possible' position. There are also some abbreviations on the map such as 'Belegt' which could mean 'occupied' or 'covered'. You can find out what the other abbreviations mean in the Military Intelligence Service 'German Military Abbreviations' Dictionary'.

The small red circle symbol can mean many different things, but in this case as it is a map of enemy defences, it is most probably an 'installation of unknown type'. The solid circle or 'red dot' appears to be "Defensive Installation- field type." The thick red lines are most probably anti tank ditches or anti tank walls. The 'smiley face' seen particularly around the centre of the position are most likely 'deployed riflemen' or 'entrenched riflemen'. The map appears to show some fairly vague positions markers, which could be camouflaged, alongside some very definite positions such as trenches and artillery. I hope this helps to identify some of the markings.

Sources:

Supplements: German Military Symbols, US Military Intelligence Research Section.

German Military Symbols 1943, US Military Intelligence Service

Company Officer's Handbook Of The German Army, US Military Intelligence Division

German Military Abbreviations' Dictionary, US Military Intelligence Service