Slovenia
So far I only visited three short sections of the Slovenian borders, which I will describe below.


Hungary-Slovenia
I only pictured one marker of this border, the very last one before the tripoint. It has "M" on one side, "RS" on the other side and "a" on the side facing the tripoint.
A map on an information sign shows that this marker will be "A1" and the next ones A2, A3 and so on.
Once this was the border of the EU, a sign still reminds us of this time. The tripoint is a nice monument. From here one can follow the border between Austria and Hungary or continue along the Slovenian-Austrian border as I will describe below.
Austria-Slovenia
From the tripoint onwards the markers start with section I, pole 1-01 presumably, but the first one I can find is 1-02. The next markers are on both sides of the path. They are marked with Oe for the Austrian side and RS for the Slovenian side. I only followed a short section, till stones I/2. Not too far away was an interesting information sign about how the border changed here in the last years.
Another section I followed is in Bad Radkersburg, starting with marker IV/31. These markers are on both sides of the river, pointing towards the border point in the middle of the river. I must have missed IV/33 somehow. Maybe it is not there anymore. IV/35 has been fallen down and is now hiding near a bench. Around the bridge that connect Radkersburg and Radgona the markers are partially harder to find and partially nicely embeded in the renoated bridge. I don't know where 38 is, but 39 is almost under the bridge.
On the other side of the bridge however there is no sign of a marker 39, but 38 is very visible. The stones IV/40 are the only ones I can find on both sides of the river. The last stone I can find along the river is IV/42 on the Austrian side of the river. I will probably be back someday, especially to visit the tripoint with Italy.