diff --git a/js/src/features/compose/controls-indicator.tsx b/js/src/features/compose/controls-indicator.tsx
index ffc0101..e46da0a 100644
--- a/js/src/features/compose/controls-indicator.tsx
+++ b/js/src/features/compose/controls-indicator.tsx
@@ -2,11 +2,12 @@ import { Video, Mic } from "lucide-react";
 import { cn } from "@/lib/utils";
 import { useMediaSettingsStore } from "@/stores/media-settings-store";
 import { Button } from "@/components/ui/button";
+import { PropsWithChildren } from "react";
 
-interface ControlsIndicatorProps {
+interface ControlsIndicatorProps extends PropsWithChildren {
   type: "reply" | "new";
 }
-export default function ControlsIndicator({ type }: ControlsIndicatorProps) {
+export default function ControlsIndicator({ type, children }: ControlsIndicatorProps) {
   const recordingMode = useMediaSettingsStore((s) => s.recordingMode);
   const setRecordingMode = useMediaSettingsStore((s) => s.setRecordingMode);
 
@@ -39,7 +40,10 @@ export default function ControlsIndicator({ type }: ControlsIndicatorProps) {
           </>
         )}
       </Button>
-      <div className="flex-1" />
+      {children ? <div className="flex-1">{children}</div> :
+        <div className="flex-1" />
+      }
+      {children && <span className="text-muted-foreground">·</span>}
       <div className="text-muted-foreground">
         Hold{" "}
         <kbd
diff --git a/js/src/features/particles/stream-view.tsx b/js/src/features/particles/stream-view.tsx
index 8fd88e7..2ffef52 100644
--- a/js/src/features/particles/stream-view.tsx
+++ b/js/src/features/particles/stream-view.tsx
@@ -9,9 +9,11 @@ import { PlaybackPageIndicator } from "@/features/playback/playback-page-indicat
 import { MediaParticleView } from "@/features/playback/media-particle-view";
 import { TextParticleView } from "@/features/playback/text-particle-view";
 import { FallbackParticleView } from "@/features/playback/fallback-particle-view";
-import { Avatar, AvatarFallback } from "@/components/ui/avatar";
+import { Avatar, AvatarFallback, AvatarGroup, AvatarGroupCount } from "@/components/ui/avatar";
 import ControlsIndicator from "@/features/compose/controls-indicator";
 import { updateStreamPlaybackMarker } from "@/lib/firestore-particles";
+import { Tooltip, TooltipContent, TooltipTrigger } from "@/components/ui/tooltip";
+import { useNetwork } from "@/hooks/use-networks";
 
 // --- Playback reducer ---
 
@@ -382,8 +384,45 @@ export function StreamView({ path, streamParticle }: StreamViewProps) {
 
       {/* Bottom overlay: stream info + reply */}
       <div className="absolute right-0 left-0 bottom-0 z-10">
-        <ControlsIndicator type={"reply"} />
+        <ControlsIndicator type={"reply"}>
+          <SeenIndicator stream={streamParticle} currentParticle={currentParticle} networkId={networkId} />
+        </ControlsIndicator>
       </div>
     </div>
   );
 }
+
+// Shows a list of avatars of users who have seen the current particle, based on playback markers in the stream particle.
+const SeenIndicator = ({ stream, currentParticle, networkId }: { stream: Particle & { type: "stream" }, currentParticle: Particle, networkId: string }) => {
+  const network = useNetwork(networkId);
+  const playbackMarkers = stream.playback_markers ?? {};
+
+  const seenUserIds = Object.entries(playbackMarkers)
+    .filter(([_, timestamp]) => timestamp.getTime() >= currentParticle.created_at.getTime())
+    .map(([userId, _]) => userId);
+
+  const seenUserEmails = seenUserIds
+    .map((userId) => network?.humans?.find((h) => h.id === userId)?.email)
+    .filter((email): email is string => !!email);
+
+  if (seenUserIds.length === 0) return null;
+
+  return (
+    <AvatarGroup>
+      {seenUserEmails.map((email) => (
+        <Tooltip key={email}>
+          <TooltipTrigger asChild>
+            <Avatar size="sm">
+              <AvatarFallback>
+                {email.split("@")[0].slice(0, 2)}
+              </AvatarFallback>
+            </Avatar>
+          </TooltipTrigger>
+          <TooltipContent>
+            <p>Seen by {email.split("@")[0]}</p>
+          </TooltipContent>
+        </Tooltip>
+      ))}
+    </AvatarGroup>
+  );
+}
diff --git a/js/src/hooks/use-networks.ts b/js/src/hooks/use-networks.ts
index a770741..7e2174d 100644
--- a/js/src/hooks/use-networks.ts
+++ b/js/src/hooks/use-networks.ts
@@ -7,3 +7,8 @@ export function useNetworks() {
     queryFn: () => apiClient.listNetworks(),
   });
 }
+
+export function useNetwork(networkId: string) {
+  const { data: networks } = useNetworks();
+  return networks?.find((n) => n.id === networkId) || null;
+}